Yet another new species from one of the best-studied neotropical areas: Plantago humboldtiana (Plantaginaceae), an extremely narrow endemic new species from a waterfall in southern Brazil

This article presents and describes Plantago humboldtiana, an extremely narrow endemic rheophytic new species from a waterfall in Corupá, Santa Catarina state, southern Brazil. The new species is unique in presenting a combination of type-G antrorse trichomes on scapes, pendulous inflorescences and 1-seeded pyxidia. Only one population is known to exist, despite intensive search efforts in nearby, similar environments. Its conservation status is assessed as critically endangered (CR) as the only known population is restricted to a dramatically small area, and is subject to extreme fluctuation due to occasional floods, and also to intense visitation by tourists, which can disturb its fragile habitat. We also present an updated identification key to the species of Plantago that occur in Santa Catarina. The recent description of three narrow endemic, threatened new species of Plantago in Santa Catarina, which is the Brazilian state with its flora best studied, highlights the need for more taxonomic research, especially in the neotropics.


INTRODUCTION
The neotropics harbour around 90,000-110,000 species of seed plants, about 37% of the world's species, and encompass widely known hotspots for conservation priorities (Antonelli & Sanmartín, 2011). However, a great many plant species in this area are threatened by habitat destruction, overexploitation, and biological invasions. The loss of this biodiversity can have disastrous consequences not only for the environment, but also for humanity (Cardinale et al., 2012;Hooper et al., 2012;Mouillot et al., 2013). Most dramatic is, however, the fact that numerous still undescribed, narrow endemic species may become extinct before they are discovered and described.
These discoveries highlight the fact that despite SC being the Brazilian state with the best-studied flora (Reis, Freitas & Cury, 2011;Sousa-Baena, Garcia & Peterson, 2014), there are still many species from this territory to be discovered and described. Furthermore, even for well-studied genera like Plantago, in well-studied areas like SC, there are considerable knowledge gaps regarding neotropical biodiversity (Hassemer, Ferreira & Trevisan, 2015;Funez, Hassemer & Trevisan, 2016;Goldenberg et al., 2016), which thwart the implementation of effective policies and measures for the conservation of biodiversity in the neotropics. Additional taxonomic research is a key approach to address the current biodiversity crisis (Agnarsson & Kuntner, 2007;Ebach, Valdecasas & Wheeler, 2011;Wägele et al., 2011;Sluys, 2013), especially in tropical and subtropical areas. Such work should include field work, thorough revision of herbarium material, and state-of-the-art molecular phylogenetic analyses.
This study fills such a knowledge gap by presenting and describing a new, extremely narrow endemic species of Plantago from a waterfall in Corupá municipality, Santa Catarina state (SC), southern Brazil, and includes a detailed description, illustrations, and an updated identification key to the species of Plantago that occur in SC.

MATERIALS & METHODS
We revised the Plantago collections at C, CGMS, DDMS, EFC, FI, FLOR, FT, FURB, GB, HAS, HBR, ICN, MBM, MVFA, MVJB, MVM, PI, SGO, TANG, UFMT and UPCB herbaria (acronyms according to Thiers, 2016). In an attempt to find any other populations of the new species, we searched on two occasions (January 2015 and February 2016) all the 14 waterfalls of the Novo River, which are all located inside the ''Reserva Particular do Patrimônio Natural Emílio Fiorentino Battistella'' particular environmental protection area in Corupá. The permission to enter and collect plants in this particular area was granted by its director, Reinaldo Langa.
The subgeneric classification of Plantago follows Rahn (1978) and Rahn (1996), with the updates of Rønsted et al. (2002), except for Littorella P.J. Bergius, which we accept as a genus distinct from Plantago (Hoggard et al., 2003). The classification of trichome types follow Rahn (1992). The assessment of the conservation status of the new species followed the IUCN (2012) and IUCN (2014) criteria. Our revised identification key to Plantago in SC updates the identification key in Rahn (1966). Unless otherwise stated, all photographs were taken by G Hassemer.
The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Code of Nomenclature for algae, fungi, and plants (ICN), and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. In addition, new names contained in this work which have been issued with identifiers by IPNI will eventually be made available to the Global Names Index. The IPNI LSIDs can be resolved and the associated information viewed through any standard web browser by appending the LSID contained in this publication to the prefix ''http://ipni.org''. The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central, and CLOCKSS.   (Fig. 4E), one of the waterfalls of the Novo River, in Corupá municipality, SC, southern Brazil (Fig. 1). Despite thorough search around all the 14 waterfalls of the Novo River on two occasions (January 2015 and February 2016, both during summer, when these plants are flowering and fruiting), not a single individual of P. humboldtiana was found outside the area of Salto Grande waterfall.
Habitat: Plants of this species grow on rocks adjacent to Salto Grande waterfall (Fig. 4). These rocks are always very humid, due to constant splashing, and are susceptible to occasional flooding, which at times eradicate most plants of this species. However, the species can survive these events, as it was found to be able to recolonise the rocks after a particularly strong flood in 2014. Conservation status: Critically endangered c[iv]). This species is restricted to a very narrow area, on a few rocks close to a waterfall (Salto Grande). This locality is included in the ''Reserva Particular do Patrimônio Natural Emílio Fiorentino Battistella'' particular environmental protection area, but nevertheless is currently threatened by on-going political and economic pressure for the construction of a dam to generate hydroelectric power (A Reis, pers. comm., 2015). This area is prone to regular flooding, to which this species is apparently well adapted. However, a more important threat to this species is the intense tourist visitation to this waterfall, as we could verify that some visitors climb the rocks around the waterfall, destroying the plants in the process. We strongly recommend that the population of P. humboldtiana be protected with a fence and protections signs. Also, the rarity and uniqueness of this species could be positively exploited to raise the awareness among the general public about the biodiversity conservation, and also for environmental education purposes.
Considering all this, we believe this species warrants a critically endangered assessment, and should be the target of ex-situ conservation efforts. We further suggest that this species be cultivated in different botanic gardens around the world, and that seeds of this species be collected in situ and cryopreserved, in order to permit the re-introduction of this species to its natural environment in the event of its extinction in nature. Observations: Plantago humboldtiana is morphologically most similar to P. australis Lam. subsp. australis, which occurs in southern South America (including southern Brazil); P. pretoana (Rahn) Hassemer, which occurs further north in Brazil in Minas Gerais, Paraná and Rio de Janeiro states (Hassemer, Trevisan & Rønsted, 2015;Hassemer et al., 2015); and P. venturii Pilg., which is endemic to Tucumán province, northwestern Argentina (Rahn, 1974). However, among these species P. humboldtiana is unique and can be promptly distinguished based on its pendulous inflorescences (Fig. 4C) and 1-seeded pyxidia. Even more unique for P. humboldtiana is its ecology: no other Plantago species worldwide is known to occur in permanently wet rocks amidst waterfalls or rapids (Fig. 4).
Plants of P. humboldtiana are striking in their pendulous inflorescences (Fig. 4C), which are a very rare character within Plantago. We could observe in many plants that, on maturity, these inflorescences bend and touch the wet stones, in this way allowing the seeds within the pyxidia to germinate and start developing roots while still attached to the mother plants' inflorescences. This feature allows this species to thrive in otherwise impossible to colonise environments such as rock amidst rapids. The only other species of Plantago that has this feature is P. corvensis, which is also endemic to SC. However, P. humboldtiana differs from P. corvensis mainly by its 1-seeded pyxidia, weakly-petiolate leaves and antrorse trichomes on scapes (Fig. 4D), whereas P. corvensis has 1-4-seeded pyxidia, distinctly-petiolate leaves and patent trichomes on scapes (Hassemer & Baumann, 2014). Furthermore, P. humboldtiana is almost rheophytic, occurring in round and permanently wet rocks amidst rapids in northern SC, whereas P. corvensis occurs in vertical rocky cliffs in southern SC (Fig. 1).

Key to the species of Plantago in Santa Catarina state, Brazil
The habitats of each species in SC are presented inside brackets (this is presented in the key only for the individual species). The species not native to SC are marked with an asterisk. This key is an updated version of Rahn (1966).