The Story of the Tulip That Went Wild: Tracing the History of Introduction of Tulipa Sylvestris in Sixteenth-Century Europe

Tulipa sylvestris, commonly called the “wild tulip”, was introduced from the Mediterranean to northern Europe in the sixteenth century and became widely naturalized. Research has focused on tulips that came from the Orient, but the introduction path of this native European, early ornamental tulip is unclear, and so is its taxonomic status: three subspecies are provisionally accepted, sometimes treated as species. Here we elucidate the history of introduction of T. sylvestris and discuss its taxonomy based on our historical �ndings. The �rst bulbs came from Bologna (northern Italy) and Montpellier (southern France) in the 1550s-1570s. Several renown botanists were involved in their introduction, namely Gessner, Wieland, Aldrovandi, De Lobel, Clusius, and Dodoens. There were various introduction routes, including one from Spain which was apparently unsuccessful. The strong sixteenth-century Flemish botanical network facilitated the introduction and naturalization of T. sylvestris across Europe. Based on the latest tulip taxonomy, the diploid subspecies australis is native in the Mediterranean, and the tetraploid sylvestris is naturalized over Europe, but our historical �ndings show that both sylvestris and australis were introduced. This underlines the need to reconsider the taxonomic status of T. sylvestris, highlighting the importance of botanical history in understanding the complex taxonomy of naturalized cultivated plants.


Introduction
Ornamental tulips were introduced to Europe from the Ottoman Empire in the sixteenth century.The tulip tradition was probably brought with the Seljuks on their migration route from Central Asia to Anatolia [1], and gained increasing popularity in Ottoman gardening and art [2].Since the establishment of the rst gardens in Istanbul in the late fteenth century and throughout the sixteenth century, several kinds of tulips were brought, sometimes in large amounts, from the empire provinces and abroad during military expeditions [1,3].For the Ottomans, tulips had a symbolic religious meaning, and became a main ornamental motif in their culture [1], prominent in horticulture and various forms of art such as pottery, tiles, embroidery, tapestry, and book illumination [2].
The tulip trend that spread in the sixteenth-century Ottoman world was soon to be expanded westwards to Europe.The Flemish Ogier Ghiselin de Busbecq (1522Busbecq ( -1592)), ambassador of the Habsburg emperor in the Ottoman court in Istanbul in 1554-1562, was long acknowledged as the rst to bring tulips to Europe.Presumably in 1554, on his way from Edirne to Istanbul, De Busbecq observed a ower unknown to him called "tulipan" by the Turks [4,5].This event, however, described in his famous Turkish letters [4], might have taken place years later, as the letters were actually written between 1581 and 1589 [6].The French diplomat and naturalist Pierre Belon (1517-1564) may actually have been the rst to bring oriental tulips to Europe [1].In 1553, he wrote about the red lilies ("lils rouges") that every Turk had in his garden [7].Belon had a garden himself, with exotic plants which he brought from his travels in the Orient during the 1540s [1,8] and distributed in his network.Once in Europe, tulips soon attracted scholarly attention.In 1559, the famous Swiss naturalist Conrad Gessner (1516-1565) observed a red tulip in the garden of Councilor Johannes Heinrich Herwart in Augsburg, a rich merchant city in Southern Germany.Two years later, he published the rst description of a tulip accompanied by a woodcut [9].Gessner's tulip was probably Tulipa suaveolens Roth., the presumed wild ancestor of "garden tulip", i.e., T. gesneriana L., a complex garden hybrid, from which modern tulip cultivars were derived [10].
Even if not the rst to bring tulips to Europe, De Busbecq did play an important role in their introduction.He sent tulip bulbs and seeds to Vienna (or brought them there himself) to the famous Flemish botanist Carolus Clusius (1526-1609), who was then curating the imperial garden [11].Clusius published the earliest tulip monograph in 1576 and amended it twice over the next three decades [12,13,14].He moved, together with his tulips, to Leiden, the Netherlands, in 1593 to take over the garden of the city's recently founded university, presently the Hortus Botanicus.Clusius' bulbs were repeatedly stolen despite his efforts to prevent theft and became a main material source for the later Dutch bulb trade [11,15].By the end of the sixteenth century, a plethora of tulip cultivars, with owers of variable colors and shapes, had made it to the gardens of royalties and nobles, collectors, scholars, amateurs and professional bulb growers.In the rst decades of the seventeenth century, the demand for tulips got absurd dimensions reaching a peak during the so-called Tulipomania, when a handful bulbs would be sold for prodigious prices [15,16].The tulip fever ceased in 1637, but it had already laid the foundations of modern international ower trade [16].
During the same period that ornamental tulips reached Europe, Tulipa sylvestris L., a small yellow tulip known then as a yellow daffodil ("Narcissus luteus"), was also introduced to northern Europe.Unlike the garden tulips that came from the Ottoman Empire, this one apparently came from the Mediterranean [17,18].It had neither the long pointy tepals that were favored by the Ottomans [2,3], nor the big cup-shaped owers that became fashionable in the West [10], but it found its way to European gardens, escaped them, and successfully naturalized.By the time Linnaeus described the species in 1753, it already deserved the epithet sylvestris, "wild".Based on the latest taxonomic treatment of the genus Tulipa, three subspecies are provisionally accepted under T. sylvestris, two of which occur in Europe: the diploid subsp.australis (Link) Pamp.(2x=24) and the tetraploid subsp.sylvestris (2x=48) [10,19].Subsp.australis is widely distributed, extending from the Mediterranean northwards to France and Switzerland and eastwards towards Belarus, Russia and Ukraine up to Central Asia [10].The native distribution of subsp.sylvestris is uncertain, suggested to be con ned to Italy, Sardinia, Sicily and NW.Libya [10].Subsp.sylvestris is widely naturalized across Europe, including France, Switzerland, Austria, Germany, Poland, Belgium, the Netherlands, Denmark, Sweden, Norway and Great Britain [20,21,22].Subsp.australis is a mountainous plant growing in poor soils, in (semi)dry grasslands, pastures and rocky areas, whereas sylvestris is primarily a plant of lowland secondary habitats, growing in rich soils and areas that have been fertilized in the past, including (remnants of) historical gardens, margins of cultivated elds, vineyards, olive groves and other orchards, grassy places, and also woods, bushes, sometimes near rivers [20,21,23,24,25,26,27,28,29].The high number of local taxa that have been synonymized under these two subspecies (e.g., T. celsiana Red., T. biebersteiniana Schult.& Schult.f., T. griesebachiana Pant., T. pumila Moench and 102 more synonyms; [22]) re ect the high morphological diversity of this species, which has the widest distribution within genus Tulipa [10].Sometimes the two subspecies are treated at the species level (e.g., [27,30].A third subspecies, subsp.primulina (Baker) Maire & Weiller, also sometimes treated at the species level (e.g., [19]), is a North African taxon and is not considered herein.
Historical research on tulips is extensive, but has focused on those species that came from the Ottoman Empire and gave birth to modern tulip cultivars.Tulipa sylvestris, however, had a different introduction route, which is poorly known and perplexed because the introduced plants became widely naturalized.Here we reconstruct the European history of introduction of T. sylvestris.We follow the journey of the rst plants that were brought from the Mediterranean to northern Europe, revealing the places, dates and botanists involved.We also discuss the species' complex taxonomy based on our historical ndings.

Methods
Literature on tulips contains a plethora of scienti c and non-scienti c sources, the latter sometimes of questionable accuracy.We therefore focused our research on original sixteenth-century textual and visual evidence, including botanical publications, herbarium specimens, collections of drawings and historical archives.Tracing botanical species in pre-Linnaean texts is challenging, as a single plant name was often attributed to several botanical species, while a single species could have many different plant names.We thus started with compiling a list of "trusted" names for Tulipa sylvestris, which we retrieved from sixteenth-century herbarium specimens, the taxonomic identi cation of which we herein veri ed.For this we searched for specimens of Tulipa sylvestris in all surviving sixteenth-century herbaria [31] for which species lists have been published and/or images of the specimens are available.Using the names of the herbarium specimens as keywords, we screened the original works of major sixteenth-century botanists, among which Clusius, Dodoens, de Lobel, Gessner and also 25 editions of Matthioli's Commentaries on Dioscorides published between 1548 and 1600 in Italian, Latin, French and German.We also considered publications of the early seventeenth century by authors active during the sixteenth century, including Johann Bauhin's Historia Plantarum Universalis which was published by his son-in-law almost 40 years after Bauhin's death [32].We also sought historical evidence of plant material exchange between southern and northern European sixteenth-century botanists in surviving archives, namely the Aldrovandian manuscripts kept at the University Library of Bologna, the digitized mail correspondence of Clusius (https://clusiuscorrespondence.huygens.knaw.nl/),and the Early modern physicians' letters of the German speaking area (www.aerztebriefe.de).Names retrieved from textual, visual and archival sources were gradually added to the list of keywords in order to achieve maximal traceability.Regarding the Aldrovandian manuscripts, we consulted the digitized volumes at http://moro.imss..it/aldrovandi/and for the undigitized volumes, we screened the manuscript titles published by Frati et al. [33] and requested to the University library of Bologna images of the originals for all catalogues of plants that Aldrovandi sent to northern European naturalists during the second half of the sixteenth century.
We also carried out observations on the morphology of Tulipa sylvestris sensu lato, using ca.400 specimens of wild and cultivated plants from around Europe, kept at Naturalis Biodiversity Center in Leiden, the Netherlands (L) and other herbaria.

Results
Early illustrations, Wieland and Gessner, 1540s-1550s The oldest surviving illustrations of Tulipa sylvestris are two watercolors contained ina two-volume handwritten manuscript from 1549, known as the Codex Kentmanus.This manuscript was compiled by the German physician Johannes Kentmann (1518-1574), who studied medicine in Padua, Venice and Bologna between 1547 and 1549.The one watercolor is named "Tulipa Turcica" and depicts a slender plant bearing a single ower with ve tepals (Fig. 1a).This unrealistic representation -monocots do not have ve tepals -is accompanied by Kentmann's uncertainty on the identity of this plant.In his annotations, probably compiled somewhat later (1550-1554), he wrote: "The Turks call this plant in their barbarous tongue 'Tulipa'; what it is I do not know" [34,35].The epithet "Turcica" implies an Ottoman origin, but all images in the rst volume of the Codex Kentmanus were drawn after plants that Kentmann observed in Italy [35].The paper sheet on which this "Tulipa Turcica" was made carries a watermark depicting a triple mountain and cross, which originates from Padua [35] (see also [36]), where Kentmann lived and drew several plants of the city's botanical garden [35].During his two-year stay, Kentmann also travelled elsewhere in Italy, observing and drawing interesting and unknown plants [34,35].The other watercolor of T. sylvestris in Kentmann's manuscript is named "νάρκισσος [nárkissos]; Lilionarcissus, Tulipae species", and depicts a robust double-owered plant (Fig. 1b).It is included in the second volume of Codex Kentmanus, which only partly contains plants that Kentmann observed in Italy [35].An Italian origin seems likely for this illustration as well, but it was unfortunately drawn on a sheet without watermark, nor is it accompanied by annotations.Therefore, we do not have actual evidence about its provenance.
Kentmann's illustrations reached the scholarly circles through the Swiss botanist Conrad Gessner (1516-1565), who borrowed Kentmann's manuscript between 1554 and 1555 [9,35].Besides publishing the rst scienti c description of a red tulip, Gessner [9] also wrote about Tulipa sylvestris based on Kentmann's "Tulipa Turcica" andacknowledged Kentmann as the source of origin for the name "Tulipa".In his notes about T. sylvestris, Kentmann [34] wrote that the name "Tulipa" is owed to the shape of the ower that refers to a Dalmatian cap ("pileoli Dalmatici"), an information that Gessner [9] and other authors later reproduced, e.g., [37,38,39].Modern authors (e.g., [1]) have argued that the name "Tulipa" derived from the Ottoman "turban" as a result of a misunderstanding, in which presumably de Busbecq was involved.But, although this information is plausible, we could not nd it in sixteenth-century literature.Referring to Kentmann's "Tulipa Turcica", Gessner [9] provided a rough morphological description of T. sylvestris and, more interestingly, mentioned that he received seeds of this plantfrom Guilandinus Borussus, the latinized name of Melchior Wieland (ca.1520-1589).Wieland was a Prussian botanist who took up his studies in Königsberg in 1544/45, continued them in Italy and settled in Padua, where in 1561, he was appointed head of the city's botanical garden, a position he held until his death [40,41].When Gessner borrowed Kentmann's manuscript he kept copies of 142 illustrations that caught his attention, among which also one of the two T. sylvestris images [42] (Figs.1a, 2a).Since Kentmann had already left Italy, Gessner asked Wieland to send him seeds of this plant from Padua.It was probably somewhere between ca.1554 and 1559 that Wieland's seeds arrived in Zurich.We base this on circumstantial evidence, as in 1554 Gessner saw Kentmann's illustration and we know that he corresponded with Wieland already since at least 1556 (Gessner to Wieland, 3rd May, 1556, www.aerztebriefe.de/id/00045404), and apparently must have hosted him in Zurich even earlier since Gessner in his letters called him his former "house guest" (hospes) [43].In spring 1559, at the latest, Wieland left Padua to embark on a ca.two-year eld trip to the Orient, as we know that in the summer of that year he had already travelled through Istanbul to Cairo (Wieland to Aldrovandi, 2 nd June, 1559, www.aerztebriefe.de/id/00016516).As far as we know, this was the rst intended introduction of T. sylvestris northwards in Europe.Gessner must have carefully studied Kentmann's illustration over the years, as can be seen in his personal notes on the illustration (Fig. 2a).He noted the morphological difference of this tulip from the (famous) red tulip that he had observed in Augsburg in 1559, and that this was rather more similar to another plant that he had received from Ulrich Fugger in 1560.He also drew Wieland's seeds on the paper sheet, and noted their morphological difference from another yellow tulip ("Tulipae luteae") that he had received from the French surgeon and collector Nicolaus Rassius (Rassé).This might have been a yellow-owered variety of T. gesneriana from Rassius' garden in Paris.
Another important botanist of the early sixteenth century, the German Leonhart Fuchs (1501-1506), also had two illustrations of Tulipa sylvestris (Table 1), but their dating as of 1543-1547 and 1543-1548 (Baumann et al., 2001) is questionable.The plant layout in the illustration dated 1543-1547 (Fig. 2b) is remarkably similar to Kentmann's "Tulipa Turcica" from 1549 (Fig. 1a), although evidently drawn by a different hand, presumably that of Fuchs' illustrator Heinrich Füllmaurer [44].It seems however unlikely that Fuchs, who never travelled to southern Europe, possessed already in the 1540s a plant still unknown to northern Europeans (see also [36] on Fuchs' misleading identi cations of Mediterranean plants).Moreover, Fuchs wrote that T. sylvestris was frequent in German gardens [44], which again is inaccurate for this early period.This observation, however, might have been written later, or referred to daffodils in general.
One more early illustration of Tulipa sylvestris survives in another handwritten manuscript of Italian origin, I Cinque Libri di Piante, compiled by the Venetian patrician Pietro Antonio Michiel from about 1550 to his death in 1576 [45].Michiel's life-long masterpiece contains images of the plants that grew in his famous garden outside Venice and in the garden of Padua, which he curated between 1551 and 1555 [45].T. sylvestris appears in this manuscript as part of a group of yellow daffodils under the name "Narcisi gialli da volgari -Tulipa spetie" (Fig. 3).Michiel wrote that this plantgrew on the Santo Angelo mountain in Abruzzo and in Bologna.A catalogue of the plants cultivated in Michiel's garden surviving in the Aldrovandian manuscripts includes several daffodil species ("Narcissi varie spes"; [46]), under which T. sylvestris is likely also meant.
Early herbarium specimens: Bologna, 1550s The oldest surviving specimens of Tulipa sylvestris also come from Italy, Bologna in speci c (Table 1).Two specimens are dated 1552 and 1553 and are included in the herbarium of Ulisse Aldrovandi (1522-1605) [47,48], one of the most prominent naturalists of the sixteenth century, appointed professor of botany in Bologna from 1561 and for the subsequent almost 40 years.In the herbarium of Aldrovandi survive eighteen in total tulip specimens, some of which originated from Bologna and others from Padua, which Aldrovandi probably received from Wieland, as evidenced from their surviving letters, which indicate exchange of plants and tulip bulbs between the two since at least 1554.The specimens of T. sylvestris both came from Bologna, the 1552 specimen representing a robust double-owered plant (Fig. 4a), and the 1553 specimen a smaller, more slender, single-owered plant (Fig. 4b).A third early specimen from Bologna is contained in the herbarium of Francesco Petrollini (Erbario B; [48, 49,50]), dated pre-1553 [51].
Six more sixteenth-century specimens of Tulipa sylvestris survive today, four of which are also Italian.One is contained in the En Tibi herbarium, also made by Petrollini around Bologna in ca.1558 [50] and another is part of an herbarium volume of unclear provenance (Erbario A), preserved together with Petrollini's Erbario B (Table 1).The two combined are conventionally known as "Erbario Cibo" [49,50].Two more specimens are dated from 1563, the rst collected by the German physician and traveler Leonhard Rauwolf somewhere in northern Italy [36], and the latter included in the surviving herbarium of Andrea Cesalpino made in Pisa for the bishop Alfonso Tornabuoni [52,53].
A specimen of unknown geographical provenance is included in the herbarium of the Swiss botanist Felix Platter dated ca.1552-1614, and a specimen of apparently French provenance is included in another Swiss herbarium, that of Caspar Bauhin from Basel, dated 1577-1624 (Table 1).
The rst scienti c description: Dodoens and the Libri Picturati, 1560s Although Gessner [9] had written about Kentmann's "Tulipa Turcica", it was in 1568 that Tulipa sylvestris was actually described for the rst time in scienti c literature.This was in the book Florum by the Flemish botanist Rembert Dodoens, latinized as Dodonaeus (1517-1585).Dodoens [37] called T. syvlestris the "small tulip" ("Tulipa minor") and published a short morphological description and a woodcut that depicts two slender, single-owered plants (Fig. 5a).Dodoens wrote that these small tulips grow somewhere in southern France.
Florum was part of a series of popular illustrated botanical books published by the famous Antwerp-based publishing house O cina Plantiniana run by Christophe Plantin.The woodcut of Tulipa sylvestris published in Florum is a mirrored copy of a watercolor (Fig. 5b) contained in the famous Libri Picturati, a magni cent collection of over 1400 plant illustrations, which is Flemish in origin and presently kept in Krakow, Poland [54].This watercolor is named "the small yellow tulip of Montpellier" ("Tulipa parva lutea.Monspel[liensis]"), a city located indeed in southern France, as Dodoens wrote.The watercolor is part of the core collection of Libri Picturati (van Uffelen, Egmond, personal communication), which is dated 1565-1568/9 [55], so it must have been shortly before 1568 that thiswatercolor was made.Indeed, in 1567, a year before Florum was published, the Mechelen-based draftsman Pieter van der Borcht (ca.1530-1608) was commissioned by Plantin to create the images that would serve as models for the woodcuts of Florum, among which also the one of T. sylvestris [56].Possibly van der Borcht did not paint the watercolor himself, but only transferred it to the woodblock [55].Another candidate maker of this watercolor is painter Jacques vanden Corenhuysewho made several plant illustrations for the Flemish nobleman Charles de Saint Omer or Karel van Sint Omaars (1533-1569), the original owner of the Libri Picturati [55].This woodcut of T. sylvestris was reprinted at least 13 times in the following 80 years [56].One more watercolor of T. sylvestris is found in the Libri Picturati and has been drawn on a paper sheet carrying a watermark from 1566 the earliest ( [57]; G. van Uffelen, personal communication), but this image does not show stylistic similarity to any of Plantin's woodcuts.
Origin France: De Lobel -Montpellier, 1560s Three years after Florum was published, another important Flemish botanist, Matthias de Lobel or Lobelius (1538-1616), wrote that he dug out bulbs of Tulipa sylvestris from the Cevennes mountains north of Montpellier and sent them to Belgium [58].De Lobel used the name "Lilionarcissus Norbonensis" (Table 1), the epithet "Norbonensis" indicating Narbone as the geographical provenance of the plant, which corresponds to Provence and Languedoc, or generally southern France."Lilionarcissus" was a name used for tulips in scholarly circles at that time [13], but was superseded by the vernacular "Tulipa"that was nally established nomenclaturally by Linnaeus [18].De Lobel probably dug out those bulbs between 1565 and 1567/8, as this period he was living in Montpellier for his medical studies and eagerly botanized the city's surroundings [59].
De Lobel mentioned that he sent the bulbs to friends in Antwerp, but who were they?Perhaps the most well-known naturalist of Antwerp was the apothecary Pieter van Coudenbergh, but unfortunately, the inventory of his famous garden [9] was published at least ve years before de Lobel sent the bulbs.It is therefore not surprising that no plant in this catalogue could be matched to Tulipa sylvestris, the closest record being a reference to three daffodil species ("Narcissi tres species"; [9]).Moreover, van Coudenbergh was not listed by de Lobel [60] among his close acquaintances, making it rather unlikely that he was the one who received the bulbs.More interestingly, de Lobel [60] mentioned in his Cruydtboeck two scribes from Antwerp who supported his work with their gardens.The rst was Willem Martini, city scribe of Antwerp since 1565, known also for his involvement in the Dutch resistance against the Spaniards.The second was Jan van Hoboken, scribe of Antwerp at a later time, 1578-1590.It seems likely that any or both of these two men received de Lobel's bulbs, but further information about their botanical activity is not known.
Besides the two Antwerp scribes, de Lobel gave a long list of plant "facilitators" in which a certain Mr. Reynoutre stands out.This name is an alias of Saint Omer, rst owner of the Libri Picturati, where the model watercolor of the Florum woodcut of Tulipa sylvestris is included.Saint Omer was a wealthy nobleman and owner of an estate and castle in Moerkerke, near Bruges in Belgium [55].Florum's watercolor, which was later reproduced also in de Lobel's (and Clusius') books published by Plantin, was made in the same period (between ca.1565 and 1568) that de Lobel dug out the bulbs in Montpellier, and this provenance is also mentioned in the watercolor's name ("Monspelliensis").It may thus be assumed that de Lobel was also the direct or indirect source of the T. sylvestris bulbs that Saint Omer cultivated in his garden, the material based on which the specieswas for the rst time described by Dodoens in 1568.
Origin Italy: Aldrovandi -Bologna and Apennines, 1570s Five years after de Lobel wrote about the Narbone tulip, he also published on the Bologna tulip, "Bononiensis Lilionarcissus luteus, sive Tulipa" [61] (Fig. 6).He wrote that the Bologna tulip looks like the Narbone tulip "in leaf, stem and ower, but it is signi cantly more vigorous and bigger", a detail of taxonomic importance as will be discussed below.He also added that the Bologna tulip was sometimes double-owered, as can be seen in herbarium specimens and illustrations of the time (Figs.1b, 4a, 6).This time, de Lobel published also two woodcuts: one for the Narbone tulip, the same as Dodoens' woodcut from Florum, and one for the Bologna tulip, representing a double-owered individual (Fig. 6).
Unlike the woodcut for the Narbone tulip, the model used for the woodcut of the Bologna tulip could not be traced among the Tulipa sylvestris illustrations and specimens that survive today.Its stylistic resemblance to Florum'swoodcut points to another, perhaps lostwatercolor that has not survived in the Libri Picturati collection presently kept in Krakow.
We do not know where de Lobel got his Bologna tulips from.They possibly grew since early in the city's gardens, as Johann Bauhin (1541-1614) reported having seen them in San Salvatore [32], one of the oldest gardens in Bologna, existing at least since the early 1550s [62].
Aldrovandi and Petrollini already possessed specimens (Table 1) before or shortly after their graduation [62], so it must have been in the study material of medical students at the university of Bologna.Nevertheless, this tulip is not easy to trace in the 1568-1582 inventory of the Bologna public garden, which Aldrovandi founded in 1568.Several yellow tulips are listed in this inventory but they are all mentioned to have a Turkish origin (Aldrovandian manuscripts Ms. 002).
What we do know is that Clusius received Tulipa sylvestris directly from Aldrovandi, as Clusius personally recalled: "It grows in abundance in the Apennines from where Ulisse Aldrovandi, the Bolognese professor, dug it out and sent it to me from Bologna, many years ago" [14].Clusius discarded de Lobel's "Lilionarcissus" in favor of "Tulipa" and used again the same woodcuts as Dodoens and de Lobel for the French and Italian plants [13,14].Clusius also suggested a new place of origin for T. sylvestris in Italy: the Apennine mountains.He rst used the epithet "Apenninea" complementary to "Bononiensis" ("Tulipa Apenninea sive Bononiensis"; [13]) and later kept only the Apennine provenance, "Tulipa Apenninea"; [14]) (Table 1), though still mentioned that he received the plant from Bologna.
In our attempt to trace when Clusius could have received the Apennine tulip from Aldrovandi, we found a catalogue dated ca.1574-1575 [63], containing a list of plants that Aldrovandi sent to Clusius for the imperial garden in Vienna (Aldrovandian Manuscripts, Ms. 136/05, cc.371-374).A certain "Tulipanum luteum" (yellow tulip) is listed therein, which may refer to Tulipa sylvestris and could be the plant that Clusius remembered having received from Aldrovandi.However, the possibility of a garden tulip variety with yellow owers (T.gesneriana) cannot be excluded.What is certain is that in 1571, Clusius had received seeds of both Bologna and Montpellier tulipsfrom one of his patrons, Jean de Brancion, a rich man from Mechelen, as Brancion himself declared in his letter to Clusius on August, 3 rd that year [64].Clusius further dispersed this material in his network.For example, in 1577 he sent bulbs of both tulips to his German friend Joachim Camerarius, instructing him how to care for these "Tulipas Bononieses"and "Mompelianas": "Do not mix them together with other tulips.Because they produce lateral bulbs and spread.It is better to put them in a distinct space […] so that they don't spread too far.Otherwise they would occupy the whole garden in a few years" [65].Clusius [13,14] repeated this observation from his own garden, that these tulips produce lateral bulbs through stolons ("tenuibus nervis in latera", "lateral nerves at the sides") and extensively spread.We do not know whether the Bologna and Montpellier tulips that Camerarius received from Clusius thrived, but eleven years later both tulips were still growing in his garden in Nurnberg [66] despite the harsh winters.Not all plant exchanges were successful though.The Dutch apothecary Willem Jasperse Parduyn (ca.1550-1603) informed Clusius in 1596 about the rotten state of most of the plants he had received, among which also the "Tulipa bononiensis" [67].The Bologna tulip was not only cultivated in northern European gardens but also Italian ones.In 1606, the prefect of the Pisa garden, Franscesco Malocchi, sent to Clusius a list of the garden's most beautiful plants, among which the "yellow scented Bologna tulip" ("Tulipa Bononiensis lutea odorata") [68].Johann Bauhin reported having received the Bologna tulips in Montbeliard, N. France, from Guillelmo Landgravio (probably William IV, Landgrave of Hesse-Kassel) and, like Clusius, he also noted the tendency of these tulipsto multiply and spread [32].The observations of these two rigorous botanists about the vegetative reproduction of T. sylvestris form the earliest evidence of naturalization for this species, a garden escape established today in the wild in many European countries.
Together with the Apennine and Narbone tulip, Clusius [14] grouped also another plant which grew on a hill close to Aranjuez, in central Spain.This "Tulipa Hispanica"was "similar to the Narbone tulip but slightly smaller".Clusius had not observed this plant during his Spanish travels, nor had he seen its ower, but got the information that the owers are dark red outside.He recalled that this plant was introduced to Belgium by the gardener Francisco de Hollebeque, a distiller from Mechelen, who became gardener of the royal garden of Aranjuez in 1580 [69].So it was probably after that year that these Spanish tulips were brought to Belgium.Clusius [14] noted the di culty to cultivate this tulip, whose bulbs only gave a single leaf and gradually perished in the Belgian environment.

Discussion
Linnaeus [18] described Tulipa sylvestris as the small yellow tulip of Italy and France ("Tulipa minor lutea italica" and "Tulipa minor lutea gallica").He copied this information from Bauhin's Pinax [17], a monumental manuscript that summarized plant names of sixteenth-century literature (Table 1).Our screening of original sixteenth-century sources revealed where exactly in Italy and France the rst bulbs of T. sylvestris came from, when, and which botanists were involved in their introduction to northern Europe.The rst material came from Italy in a still early period for botany as a eld study [70]; Between ca.1554 and 1559, Wieland, sent seeds from Padua to Zurich, to Gessner.The latter was at that time the most famous naturalist beyond the Alps, and by sending him tulip seeds Wieland possibly hoped to increase his status in the botanical scene (which he achieved shortly after, in 1561, when he became the prefect of the Padua garden).Wieland may have received his material from Bologna, from his friend Aldrovandi, who already had access to this plant in the early 1550s.We do not know, however, if Wieland's seeds ever grew into owering plants in Gessner's garden or if any derived plant material was further dispersed by Gessner to fellow naturalists.Growing tulips from seed to ower takes years, and in 1561 Gessner reported only the receipt of the seeds.And four years later, in 1565, he died.Around that year, de Lobel "opened" the second introduction path, from France, and was acknowledged by Clusius [14], the most in uential man in tulip history, as the rst who introduced T. sylvestris to northern Europe.In 1576, de Lobel also coined the name "Bologna tulip", but the source of his Bologna tulips remains unclear.Possibly it was again Aldrovandi, either directly or indirectly through their common network.Throughout the second half of the sixteenth century, Aldrovandi sent material of numerous plant species to his northern European correspondents.A plethora of plant catalogues kept in his surviving manuscripts in Bologna are evident of these exchanges [33].De Lobel had lived in Bologna where he had met Aldrovandi and acquired from him both plants and botanical knowledge [60].About T. sylvestris, however, de Lobel did not mention such information, nor is any plant exchange between the two men found in the surviving Aldrovandian manuscripts.Among the plant suppliers that de Lobel [60] mentioned in the introduction of his Kruydtboek, we also nd de Brancion, who vigorously exchanged plants with Aldrovandi between ca.1563 and 1568 [71].Based on the surviving Aldrovandian manuscripts, de Brancion was the only Flemish (besides Clusius) with whom Aldrovandi exchanged plant material.De Brancion was a close friend of Clusius [55], to whom he had sent T. sylvestris [64] and also of Dodoens [72].Within this network, de Brancion could have received the Bologna tulips from Aldrovandi and sent them to de Lobel, but no actual evidence was found that supports this hypothesis.Clusius [14] reported having received T. sylvestris from Aldrovandi from Bologna, from material originating from the Apennine mountains, an event that possibly happened in the 1570s.Other introduction events have also happened.Plants with more reddish-tinted owers were introduced from Spain [14], but apparently did not ourish in northern European gardens.Totally different introduction paths are also possible.For instance, it has been suggested that Tulipa sylvestris, being a weed of vineyards, was unintentionally introduced northwards in Europe through the grapevine export, perhaps already since Roman times [1].This path could have acted complementarily to the intended introduction of sixteenth-century naturalists.It is even possible that also bulbs of T. sylvestris were among the numerous kinds of tulips that arrived from the Ottoman empire to Italian gardens in the early 1550s, as Kentmann's "Tulipa Turcica" and the 1568-1582 Bologna garden inventory imply.
Whatever the routes of introduction of Tulipa sylvestris may have been, it was the strong sixteenth-century Flemish botanical network, supported by Clusius, de Lobel, Dodoens, Plantin and their rich friends with gardens, such as Saint Omer and de Brancion, which facilitated the introduction of T. sylvestris and its spread in Europe.This network was supplied with Mediterranean plant material from two main centers, southern France and northern Italy, which were popular botanical destinations for northern European naturalists [70].Aldrovandi from Bologna was a direct source of such material [33].Clusius had a large network of correspondents in Europe to whom he sent tulip bulbs [73], so we may expect that he distributed bulbs of T. sylvestris to more correspondents than those reported herein.Archives and letters between sixteenthcentury naturalists contain plenty of references to exchanges of bulbs, tulips and daffodils, under which T. sylvestris may also be meant.Unfortunately, in most cases these vague plant names could not be linked to botanical species.It was with de Lobel's works [58, 61] that it became evident that a group of tulips, in fact T. sylvestris, grew wild in European (Mediterranean) ground.De Lobel's epithets "Bononiensis" and "Narbonensis" and Clusius' "Hispanica" clearly separated T. sylvestris from the exotic garden tulips that were imported from the Ottoman empire.The Bologna origin persisted in literature and almost a century after, T. sylvestris is explicitly indicated as the Bologna tulip in the 1657 inventory of the Bologna public garden ("Tulipa ore luteo minor Bononiensis"), unambiguously distinguished from the several garden tulips of various colors and shapes ("Tulipanorum variae species, & variorum colorum") [74].On the other hand, the evidence that has reached our days is dominated by the large archives of Clusius and Aldrovandi.If more information had survived about Wieland, Dodoens, de Lobel or other naturalists, we may have had another view of the introduction history of T. sylvestris.
The sixteenth century was the time when the study of plants shifted from a focus on medicinal uses to an interest on plant diversity and taxonomy [50,75,76].Tulipa sylvestris, and tulips in general, do not possess medicinal properties and were probably of no interest to classical authors and their successors.It is therefore no wonder, that Pietro Andrea Matthioli, the ultimate botanical authority of the sixteenth-century and faithful follower of Dioscorides, wrote nothing about tulips.The interest on plants as direct object of study was gradually shaped in the course of the century.It would be no exaggeration to say, that this reformation took place in parallel with the introduction of tulips in Europe; these owers of unprecedented beauty and no apparent use, other than ornamental.Matthioli did publish woodcuts of tulips, though, some of which imaginary, in his chapter about daffodils.Only after Matthioli's death, his opponents dared to publish their amended versions of Matthioli's Commentaries [75].In such an occasion, Camerarius [77,78] suggested that a multi-branched daffodil of Matthioli may have actually been T. sylvestris, and he published a woodcut of the species representing a triple owered plant (Table 1).
Connecting our historical ndings with the current taxonomy of Tulipa sylvestris, we get some interesting insights.Based on the species' current subspeci c circumscription, the plants that are naturalized over Europe belong to the tetraploid subsp.sylvestris, while the plants that are native in the Mediterranean region belong to the diploid subsp.australis [10].Subsp.sylvestris is apparently native also in (parts of) Italy [10,80].Our ndings, however, show that actually both subspecies have been introduced to the north.From the overview of historical literature, we obtained several places of origin for T. sylvestris: the Cevennes mountains in southern France, Bologna and the Apennine mountains in northern Italy, and Aranjuez in central Spain.Looking into the taxa that grow today in these regions, we see that only the plants that grow around Bologna belong to subsp.sylvestris.The tulips that grow in the Cevennes, Apennines and Aranjuez belong to subsp.australis [23,24,80,81, 82] (Fig. 7).If any bulbs of T. sylvestris did come to Italy from the Ottoman empire, then these would have likely also been subsp.australis [83].
Interestingly, de Lobel [61] had noticed that the Bologna tulip is bigger than the French one.One of Clusius' correspondents, Parduyn [67], also noted the distinctiveness of the Bologna tulip (subsp.sylvestris) from the French and Spanish one (both subsp.australis) "Tulipa bononiensis diversa ab hispanica et narbonensi" ("the Bologna tulip, which is different from the Spanish and Narbone tulip").Indeed subsp.sylvestris has been suggested to be an autotetraploid derived from the diploid subsp.australis ( [10,24], see also [80]), and as such it is expected to be larger in size.On the other hand, subsp.sylvestris grows in richer soils than subsp.australis, another factor that favors a larger plant size.Female sterility was also suggested to affect plant size in subsp.sylvestris [84].De Lobel also noticed that the Bologna tulip is more vigorous ("vegetatiora") than the French one, which may imply that the former plant can easier establish in a garden.He further wrote that Bologna tulips were sometimes double-owered, a character which may also be connected to their tetraploid nature.Sixteenth-century plants from Italy were mostly visualized by double-owered individuals (Fig. 1b, 4a), sometimes even triple (Table 1).Nevertheless, populations of subsp.sylvestris have mostly single-owered plants, the division of the stem being rather a random, infrequent event.Apparently, the multiple owers were a desired character for ornamental purposes.In fact, subsp.sylvestris may have been a naturalized cultivated plant also in Bologna, as it occurs in the city environs only in secondary habitats, and its native occurrence has been questioned [23,80].Already since the sixteenth and seventeenth century it was reported being cultivated in the gardens of Bologna and other Italian cities [32,68,74].It could even be that the tetraploid Bologna tulip derived from material that was brought to the city's gardens from the Ottoman empire in the 1540s-1550s.The two subspecies have distinct ecological and altitudinal preferences and do not co-occur in the wild.The different forms illustrated in sixteenthcentury literature, slender vs. robust, single-vs.multi-owered plants (Table 1, Figs. 1,4,6), may correspond to these two subspecies, the diploid australis and the tetraploid sylvestris, but this is not always straightforward.Since both subspecies were brought together in sixteenthcentury gardens, we would expect that triploids also occur around Europe, which is supported in literature [28,85].
The Apennine origin of Clusius [14] is somewhat enigmatic.Clusius lumped together the Apennine and Bologna tulips (Table 1) [12,13,14], but the rst should belong to subsp.australis and the latter to subsp.sylvestris.One could assume that the Apennine origin was a misunderstanding of Clusius and that Italian plants came only from Bologna.Indeed, Clusius [14] wrote that the Narbone tulip looked like the Apennine tulip, but it was "generally smaller", a statement that seems confusing considering that the australis plants of the Cevennes would not be smaller than the (also australis) plants of the Apennines, but they would be smaller than the sylvestris Bologna plants.In physically examining the two specimens preserved in Aldrovandi's herbarium in Bologna, we noted that only one of them (Fig. 4b) can be identi ed with certainty as subsp.sylvestris.The other specimen (Fig. 4a) can rather be identi ed as subsp.australis [26,27,28], but depending on the identi cation source used it can also fall within the range of both australis and sylvestris [21] or even be sylvestris [86].Clusius [14] also wrote that the owers of the Narbone tulips were greener outside compared to the Apennine tulips.This statement adds to the confusion, considering that the owers of the plants that grow (in abundance) in the Cevennes are reddish outside, and not greenish ( [21], F. Hopkins personal communication).Plants with greenish outer tepals that belong to subsp.sylvestris are said to grow in the area, but are hard to nd (F.Hopkins, personal communication).The Libri Picturati watercolor, which is probably a plant from the Cevennes, rather has greenish-red tepals (Fig. 5b).Actually, among sixteenth-century representatives of Tulipa sylvestris, only Clusius' "Tulipa Hispanica" was mentioned to have reddish color in the outer tepals [14], which is a main discriminant character for subsp.australis vs. sylvestris in modern oras, including the Spanish one [81].
The above make evident that the currently accepted distinction of subsp.sylvestris as a naturalized tetraploid in (northern) Europe and subsp.australis as a native diploid in the Mediterranean (up to Central Asia) does not conform with the history of introduction of Tulipa sylvestris, because both diploid and tetraploid plants have been introduced northwards to Europe.The introduced plants came from three or four different locations in Italy, France and Spain and are morphologically variable, although probably Spanish plants did not ourish after their introduction (Fig. 7).A new taxonomic assessment of Tulipa sylvestris is needed.This will be the next step of our research, employing genomics, morphometry and ploidy.
We suggest that a combination of botanical and historical research is necessary in order to understand the complex origin and taxonomic status of naturalized plants that have a past of introduction.Recent studies point to the same direction [87,88,89,90].Large-scale initiatives of the last decades to digitize historical archives, books and herbaria, and make them publicly available online pave the way for such interdisciplinary studies [50,89,91].Establishing global open-access databases with more historic material can provide new tools for research in botanical history [90].Physical access to the original material remains essential for observing details, as conducted herein for example to verify the taxonomic identi cation of Aldrovandi's ca.470-year-old herbarium specimens.Nevertheless, our focus in botanical history studies should be (remote) research on digitized images, as this enormously facilitates the study and accessibility of valuable treasures of our botanical heritage, without the risk of damaging them.

Figure 5 French
Figure 5