﻿Notes on Strobilanthes (Acanthaceae) with capitate inflorescences in Thailand

﻿Abstract Twenty-three species of Strobilanthes Blume with capitate inflorescences are enumerated in Thailand. Strobilanthesphengklaii Kladwong & Chantar., a new species from North-eastern Thailand, is described and illustrated. Strobilanthespaniculiformis J.R.I.Wood, S.phyllostachya Kurz and S.squalens S.Moore are new records in Thailand. Strobilantheskerrii Craib is reinstated, and S.evrardiivar.parviflora J.B.Imlay, S.bombycina J.B.Imlay, Hemigraphishispidula Craib and Sericocalyxthailandicus Bremek. are treated as new synonyms. 19 taxa are lectotypified. A key to species, taxonomic notes and photographs are provided as well as a preliminary conservation assessment and distribution maps.


Introduction
Strobilanthes Blume is a genus of Acanthaceae consisting of ca.454 species mostly distributed in tropical and subtropical Asia (Mabberley 2008;Christenhusz et al. 2017;Tripp et al. 2021;POWO 2023;WFO 2024).Strobilanthes species are herbs, subshrubs, shrubs or small trees, rarely plants are creeping.Many species are gregarious, and some have a plietesial life cycle, living several years before flowering and then, once having flowered, dying (Beentje 2016).This genus is unique in having the rugula and trichomes retaining the style (Fig. 6F) on the inner surface of posterior corolla (Wood, 1994b;Carine and Scotland 2002;Moylan et al. 2004;Wood and Scotland 2009;Hu et al. 2011;Tripp et al. 2021;Kladwong and Chantaranothai 2022).
Furthermore, three inflorescence types, spicate, paniculate and capitate are found in Strobilanthes species.This informal grouping as used by Wood and Scotland (2003b), Hu et al. (2011) and Kladwong and Chantaranothai (2023) but is not used in other treatments, e.g., Bremekamp (1944), Wood (1994b).The informal grouping may not work throughout the range of Strobilanthes, but it does provide a robust way of identifying Thai species.In the capitate type the PhytoKeys 244: 89-126 (2024), DOI: 10.3897/phytokeys.244.124260 Pornchai Kladwong & Pranom Chantaranothai: Notes on Strobilanthes (Acanthaceae) with capitate inflorescences in Thailand flowers are clustered towards the tips of the strongly abbreviated inflorescence axes, and the involucral bracts and flowers are densely arranged.The bracts are variable in size and shape with the outer bracts generally larger than the inner ones (Bremekamp 1944;Bennett and Scotland 2003;Wood and Scotland 2003b;Hu et al. 2011;Kladwong and Chantaranothai 2023).A species list of all three groups based on inflorescence types reported in Thailand is presented in Table 1.
Table 1.List of species in the three groups of inflorescence types present in Thailand.During the preparation of the taxonomic account of Strobilanthes for the Flora of Thailand we recently reported six Thai Strobilanthes species with paniculate inflorescences (Kladwong and Chantaranothai 2023).Taxonomic work on the spicate species is ongoing and this paper enumerates the 23 native species and one subspecies of the capitate group in Thailand.Six species are endemic in Thailand.A new species of Strobilanthes is described and three species are newly recorded.The identification key and nomenclatural treatments are presented.

Notes on taxonomic characters
The unequal leaf pairs are observed in many species of Strobilanthes (Wood 1994b;Hu et al. 2011).This character is variable in some species, but it can be used to group S. articulata, S. phyllocephala and S. falconeri.The bracts are commonly used to distinguish species, especially using shapes, sizes and indumentum types (Clarke 1884;Bremekamp 1944;Wood 1994b;Bennett and Scotland 2003;Hu et al. 2011).Moreover, the occurrence of leaf-like bracts or the bract having a petiolar base (Bremekamp 1944;Wood and Scotland 2009;Hu et al. 2011) are also used to recognize the species such as S. brandisii, S. consors, S. cruciata, S. erecta, S. esquirolii, S. falconeri and S. phyllocephala.The calyx is useful for taxonomic delimitation (Nees 1832;Bremekamp 1944;Wood and Scotland 2003a;Hu et al. 2011).The calyx lobes are subequal in almost all species whereas they have one lobe longer than others in S. dimorphotricha and S. paniculiformis.The colour of corolla is usually purple or pale purple or mauve or pale blue, but rarely white or yellow (Benoist 1935;Imlay 1938Imlay , 1939;;Bennett and Scotland 2003).The white corolla is found only in S. cruciata.Purple and white can occur in species such as S. kerrii and S. speciosa.The yellow corolla is rare, and this character is observed in S. phengklaii, S. squalens and S. phyllostachya.

Conservation assessments
23 species of Strobilanthes with capitate inflorescences are enumerated in Thailand.Three species, S. chiangdaoensis, S. paniculiformis and S. phyllostachya are assessed as vulnerable.Two species, S. graminea and S. hypomalla are endangered.All localities of the threatened species are in protected areas such as the national park and wildlife sanctuary, but they have only a few records.Moreover, they also need specific habitats such as the rugged limestone ridge in mixed evergreen and deciduous forests or the open plateau of evergreen mountains and the sandy soil in dipterocarp forest.The changes of habitats are occurring through increasing droughts and fires caused by humans leading to the decline of the threatened species.Strobilanthes chiangdaoensis and S. phyllostachya are cultivated at Queen Sirikit Botanic Garden.Strobilanthes articulata and S. phengklaii, S. phyllocephala are Data Deficient with few collections; more field work is needed to assess these species.Further details on conservation assessments of the threatened species are provided under the species accounts below.Hance 536 from CAL [CAL0000019794] was designated as the lectotype of Gutzlaffia aprica by Albertson and Wood (2012).On examination, we found a duplicate of this collection deposited at GH [GH00387581].The specimen has Hance's handwriting as follows: Gutzlaffia aprica Hance.This specimen has branches, leaves and inflorescences, and it is the best preserved.

Key to the species of Strobilanthes with capitate inflorescences in
The original protologue of Gutzlaffia pedunculata was based on Kerr 1430 (Craib 1911).We found that this collection has six duplicates.Two sheets are deposited at K [K001514863, K001514864] and one is housed at each of BM [BM000796839], C [C10005192], L [L2832219] and P [P00719397].All duplicates are in good shape.We select K001514863 as the lectotype because it has more mature leaves, inflorescences and flowers.Distribution.Endemic to Thailand.

Strobilanthes articulata
Ecology.In evergreen forest, often on rocks; 1,300 m alt, flowering and fruiting December.
Preliminary conservation status assessment.This species is only known from its type locality and is assessed as Data Deficient (DD) following IUCN (2022).More field work is needed to assess the conservation status of S. articulata.
Notes.Strobilanthes articulata superficially resembles S. dimorphotricha Hance in having zigzag stems in the upper parts, strongly unequal leaf pairs and glabrous and caducous bracts, but it differs in having no bracteoles vs. present in S. dimorphotricha.
Strobilanthes articulata was described by Imlay (1939) based on Kerr 9630 which has seven duplicates.Two of which are at K [K001096856, K001096857] and one at each of ABD [ABDUH:2/887], BK [257638], BM [BM001191001], C [C10005193] and KYO.BM001191001 has Imlay's handwriting as follows: "Strobilanthes articulata Imlay Type no.", and it also has the mature fruit and corolla which correspond with the protologue.Therefore, we select it as the lectotype.Kerr 16335 was mentioned as the type of S. evrardii var.parviflora (Imlay 1939).The type has three duplicates, one at each of ABD [ABDUH:2/906], BM [BM000906338] and K [K001514907].BM000906338 has Imlay's handwriting as follows "Strobilanthes evrardii R. Ben.var.parviflorus J.B.Imlay Type no. of var.".Additionally, this specimen has a flower and the corolla length that agrees with the protologue.Therefore, the sheet BM000906338 is selected as the lectotype.

Strobilanthes brandisii
We examined the type of S. evrardii var.parviflora and found it conspecific with S. brandisii.
Notes.Strobilanthes capitata resembles S. kerrii Craib and S. speciosa Blume in having a straight corolla and nodding short stamens.The species differs from the former as it lacks purplish hairs on the stems, petioles and peduncles and from the latter by having ovate or oblong-elliptic and curved bracts and blue to purplish-blue flowers.
Nees (1832) described Goldfussia capitata based on Wallich 2351 which has five duplicates, one at each of BM [BM000793162], K [K000883084] and K-W [K001115708] and two at GZU [GZU000251594, GZU000251595].The sheet K001115708 is the best preserved and has completely mature leaves, inflorescences and flowers.Therefore, we select it as the lectotype.Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 19,556.802km 2 and an Area of Occupancy (AOO) of 32.000 km 2 and is assessed as Vulnerable (VU), B1 a, b (i, ii, iii) following IUCN (2022).This species grows among rugged limestone rocks which occur at the top of limestone mountain.This habitat is subject to increasing droughts and fires leading to decline of S. chiangdaoensis.
Notes.Strobilanthes chiangdaoensis resembles S. esquirolii in having oblong-lanceolate bracts and bracteoles.However, the bracts and bracteoles of S. chiangdaoensis are glabrous or sparsely hairy on the adaxial surface and pubescent on the abaxial surface vs. sericeous on both surfaces in S. esquirolii.Moreover, the capsules of S. chiangdaoensis have two seeds with two lower rudimentary ovules vs. four seeds without rudimentary ovules in S. esquirolii.
Ecology.In evergreen forest, granite bedrock; 250-2,500 m alt., flowering and fruiting from September to May.
Selected specimens examined.Notes.Strobilanthes dimorphotricha subsp.rex differs consistently from subsp.dimorphotricha Hance from China and Vietnam in the rigid and subequal or sometimes unequal leaves.Subsp.rex appears similar to S. paniculiformis J.R.I.Wood in which the calyx lobe has 1 lobe longer than others.However, it differs by having ovate or elliptic-lanceolate bracts vs. ovate-orbicular in S. paniculiformis.Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 469,202.533km 2 and an Area of Occupancy (AOO) of 88.000 km 2 and is assessed as Least Concern (LC) following IUCN (2022).

Strobilanthes echinata
Notes.Strobilanthes echinata differs from S. cruciata in its dentate or fimbriate or dentate-crenate vs. acuminate on the apex bracteoles and calyx.In addition, the bracts of S. echinata are sessile vs. bract with petiolar base in S. cruciata.
Strobilanthes maingayi was described based on Maingay 1182 at K (Clarke 1884).Material at K was considered to be the holotype by Bennett et al. (2008).However, there is no indication in Clarke (1884) that only the material now in K was studied.We also found that there are three duplicates of Maingay 1182, two of which are deposited at K [K001514853, K001514854] and the other one at BM [BM00088495].K001514853 has more leaves and inflorescences than the others.Bennett et al. (2008) can be considered as first step lectotypification (Turland 2019).We therefore, undertake the second step and select K001514853 as the lectotype.
Kerr 19190 was cited in the protologue of S. latibracteata (Imlay 1939).This number has three duplicates each one was deposited at ABD [ABDUH:2/908], BK [257645] and BM [BM000793157].We found that the sheet BM000793157 has Imlay's handwriting labelled as "Strobilanthes latibracteata Imlay Type no." and the specimen has well-preserved bracts as well as corolla.Furthermore, the size of the leaf, bract and corolla matches with the protologue.Therefore, the sheet BM000793157 is selected as the lectotype.
Kerr 10835 was mentioned as the type of S. maingayi var.glabra (Imlay 1939).[The varietal name was originally published as 'glaber: but as Strobilanthes is feminine we follow Bennett et al. 2008  Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 312,285.154km 2 and an Area of Occupancy (AOO) of 44.000 km 2 and is assessed as Least Concern (LC) following IUCN (2022).
Notes.Strobilanthes erecta resembles S. phyllocephala J.R.I.Wood & Scotland in the shape of its leaf base, but it differs in having ovate-elliptic or obovate and caducous bracts.Wood and Scotland (2006) treated S. laotica as a synonym of S. dimorphotricha subsp.rex, but after investigation of type specimens we found that this species is conspecific with S. erecta.This is corresponded with the report of Son et al. (2018).Son et al. (2018) proposed the duplicate of Put 3302 from K (without barcode) as the lectotype of S. suborbicularis.Unfortunately, we have not seen this duplicate.Moreover, they also provided a picture of the lectotype, but we found that this picture is the sheet BM000906322 at BM, not K: the citation of K may therefore be in error.We  Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 195,058.419km 2 and an Area of Occupancy (AOO) of 68.000 km 2 and is assessed as Least Concern (LC) following IUCN (2022).
Notes.Strobilanthes esquirolii resembles S. brandisii and S. consors in having a densely white tomentose indumentum on bracts, bracteoles and calyx, but it can be distinguished from both in having sulcate stems, oblong-lanceolate bracts.In addition, S. esquirolii is also different by dark green stems and bracts.Craib (1914) described S. leucocephala based on Kerr 2317 which has seven duplicates, four in K [K001514900, K001514901, K001514902, K001514903] and one in each of BM [BM000906289], E [E00133531] and TCD.K001514901 has more inflorescences and flowers than the others; therefore, we select this specimen as the lectotype.
We have examined the types of S. bombycina and S. esquirolii and found that they are conspecific because they are densely white tomentose on bracts, bracteoles and calyx and the bracts are oblong-lanceolate.The original protologue of S. bombycina was based on Kerr 10211 (Imlay 1939)  Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 69,009.843km 2 and an Area of Occupancy (AOO) of 36.000km 2 and is assessed as Least Concern (LC) following IUCN (2022).
Notes.Falconer 423 was mentioned in the original protologue of S. falconeri (Anderson 1867).There are three duplicates two at CAL [CAL0000019638, CAL0000019639] and one at K [K000882995].All the specimens were labelled as "Strobilanthes falconeri T.Anderson" in Anderson's handwriting.The sheet CAL0000019638 has more leaves, inflorescences and fruits.Therefore, we select this specimen as the lectotype.
This species was formerly known only from Myanmar, but is now known from the Northern, South-Western and Central floristic regions of Thailand.Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 3,865.766km 2 and an Area of Occupancy (AOO) of 16.000 km 2 and is assessed as Endangered (EN), B1 a, b (i, ii, iii) following IUCN (2022).This species grows on open limestone hills and is only recorded from a few records.The changes of the habitat through increasing droughts and fires are likely to lead to decline of S. graminea.

Strobilanthes graminea
Notes.Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 10,177.798km 2 and an Area of Occupancy (AOO) of 16.000 km 2 and is assessed as the Endangered (EN), B1 a, b (i, ii, iii) following IUCN (2022).This species grows on sandy soil in dipterocarp forest and is only recorded from a few records.The changes of the habitat through increasing droughts and fire are likely to lead to the decline of S. hypomalla.
Notes.Strobilanthes hypomalla resembles S. aprica, but differs in having greenish or yellowish green stems, linear-lanceolate leaf shape, and the outside of the corolla is pubescent.Moreover, the pollen of S. hypomalla is prolate or subprolate with a 3-colporate aperture and longitudinal spinose ribs on the exine sculpturing as opposed to 3-cryptoaperturate and with short conical spines over the exine in S. aprica (Kladwong and Chantaranothai 2022).According to the protologue of S. hypomalla, the corolla was described as glabrous outside but the specimens from Thailand show that it is pubescent.Further research based on more specimens is needed to comprehend this variation.Goldfussia kerrii (Craib) Bremek., Verh. Kon. Ned. Akad. Wetensch., Afd. Natuurk., Sect. 2. 41: 231. 1944. Goldfussia lanuginosa Bremek., Dansk Bot. Ark. 23: 276. 1966 Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 80,801.690km 2 and an Area of Occupancy (AOO) of 52.000 km 2 and is assessed as Least Concern (LC) following IUCN (2022).

Strobilanthes kerrii
Notes.Strobilanthes kerrii has many characteristics in common with S. capitata and S. speciosa, especially the leaf and bract shapes and inflorescence type.However, it can be distinguished due to the presence of rigid dark red trichomes on stems, petiole and peduncle that are absent in S. capitata and S. speciosa.Strobilanthes kerrii was treated as a synonym of S. speciosa (Bennett and Scotland 2003), but now we conclude that it should be regarded as species in its own right.
This species was described by Craib (1912) based on Kerr 988 which has five duplicates, three of them were deposited at K [K001514920, K001514921, K001514922] and each one kept at BM [BM000793163], E [E00136697] and TCD.All are in good shape, but the sheet K001514920 has more mature leaves and flowers.Therefore, we select this specimen as the lectotype.
Helfer's collection was cited in the protologue of S. subcapitata (Clarke 1884).This collection has three duplicates.Two of which were deposited at K [K000883112, K000883113] and one housed at P [P00719448].Both the duplicates at K have Clarke's handwriting as follows: "Strobilanthes subcapitata Clarke": but K000883112 has more mature leaves.Therefore, we select this specimen as the lectotype.
The original protologue of S. microcephala was based on Poilane 15853 (Benoist 1934).This collection has five duplicates one at A [A00286779], two at K [K001514870, K001514871] and two at P [P00719373, P00719376].P00719373 has more mature leaves and inflorescences; therefore, it is selected as the lectotype.The others are isolectotypes.Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 12,195.648km 2 and an Area of Occupancy (AOO) of 12.000 km 2 and is assessed as Vulnerable (VU), B1 a, b (i, ii, iii) following IUCN (2022).This species grows on the open plateau of evergreen mountains and is recorded from only a few collections.The changes of the habitat through increasing droughts and fire might lead to causing decline of S. paniculiformis.
Notes.Strobilanthes paniculiformis was formerly known from the Naga Hills of Eastern India was also recently recorded in the Kachin State and Sagaing Region of Myanmar (Wood et al. 2022) but is now seen to have a wider distribution stretching into the Northern and North-Eastern floristic regions of Thailand.Description.Herbs up to 40 cm tall, perennial, erect or decumbent, anisophyllous.Stems 4-angled, sulcate or subterete when mature, pubescent or glabrescent.Leaves petiolate; blades lanceolate to oblong-lanceolate, 1.8-10 × 0.6-3.5 cm, hairy on adaxial surface, pubescent on abaxial surface, lateral veins 3-7 pairs, prominent on both surfaces, apex attenuate to caudate, base attenuate, and decurrent onto petiole, margin serrate or crenate, ciliate; petiole 0.3-2.5 cm long, pubescent.Inflorescences terminal capitate, 3-5-flowered; peduncle absent; bracts lanceolate or linear-lanceolate, 5-13 × 2-4 mm, persistent, the outer one longer than the inner, white sericeous on both surfaces, the upper part sparsely hispid, apex obtuse, margin entire or obscurely serrate, base sessile, ciliate; bracteoles linear, 3-5 × ca.0.8 mm, white sericeous on both surfaces.Calyx 5-lobed; lobes linear, 4-5 × 0.5 mm, subequal, apex acute, white sericeous on both surfaces.Corolla yellow, funnel shaped, 2-4 cm long, densely white sericeous on top at bud, sparsely pubescent at anthesis, glabrous inside except hairs retaining style; tube yellow, cylindric for 4-6 mm long; mouth 1-1.5 cm wide; lobes 5, ovate, 3-4.5 × 3.5-5 mm, apex obtuse.Stamens 4, included, didynamous; short filaments 2 mm long, long filament 3-5 mm long, all filament straight and glabrous; anther thecae ca.1.5 mm long, white, without spur; pollen 3-colporate, prolate or subprolate in equatorial view, circular in polar view, polar range 51-67 μm, equatorial range 31-41 μm; ectoapertures fusiform; exine divided into longitudinal ribs, each rib with a coarse ladder-like reticulum.Ovary ellipsoid, 2 mm long, densely white sericeous at apex; style 2.5-3 cm long, puberulous.Capsule fusiform, 5-7 × 3-4 mm, white sericeous, 4-seeded.Seeds ovate in outline, ca.1.8× ca.1.5 mm, hairy.Preliminary conservation status assessment.This species is only known from two populations suggesting that this species is endemic to the north-eastern floristic region of Thailand.It is assessed as Data Deficient (DD) following IUCN (2022).However, S. phengklaii was legally collected from a protected area and it is recorded as common in the locality.Strobilanthes phengklaii has a few records.The changes of the habitat through increasing droughts and fire is likely to lead to the decline of this species.More field work is needed to assess the conservation status of S. phengklaii.Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 10,101.500km 2 and an Area of Occupancy (AOO) of 28.000 km 2 and is assessed as Vulnerable (VU), B1 a, b (i, ii, iii) following IUCN (2022).This species grows near streams in evergreen forest or bamboo forest with a few records.The changes of the habitat through increasing droughts and fire are likely to lead to the decline of S. phyllostachya.

19.
Notes.Strobilanthes phyllostachya is distinguishable from S. squalens S. Moore by its elliptic bract and hairlessness on the outside of the corolla.This species was formerly only known from Myanmar (Kurz 1871;Wood et al. 2022), but is now newly recorded from the Northern and Southwestern floristic regions of Thailand.Preliminary conservation status assessment.This species has an Extent of Occurrence (EOO) of 399,832.702km 2 and an Area of Occupancy (AOO) of 100.000 km 2 and is assessed as Least Concern (LC) following IUCN (2022).
Hemigraphis hispidula was described by Craib (1913).However, after investigation of type and non-type specimens from Thailand, we find that this species has many characteristics in common with S. serpens.Therefore, H. hispidula is placed as a synonym of S. serpens.The original protologue of H. hispidula was based on Kerr 2383 and Kerr 2383a (Craib 1913).There are two duplicates of Kerr 2383 one at E [E00273430] and the other at K [K000882584] and there are two duplicates of Kerr 2383a one at E [E00273431] and the other at K [K000882585].All are in good shape: we designate the sheet K000882585 as the lectotype because it has more mature stems and leaves.

Figure 1 .
Figure 1.Strobilanthes brandisii T.Anderson A stem and leaves B inflorescences C corolla, side view D corolla and stigma.

Figure 5 .
Figure 5. Strobilanthes kerrii Craib A adaxial surface of leaves B abaxial surface of leaves C-F inflorescences and corolla.

Diagnosis.
Similar to S. brandisii T.Anderson and S. esquirolii H.Lév. in having single capitate inflorescences, sessile or subsessile and densely white sericeous bracts but differs in having lanceolate or linear-lanceolate bracts and yellow corolla vs. spathulate bracts and purple corolla in S. brandisii and oblong-lanceolate bracts and violet corolla in S. esquirolii.The morphological difference among S. brandisii, S. esquirolii and S. phengklaii are presented in Table2.

Figure 8 .
Figure 8. Strobilanthes phyllostachya Kurz A stem B leaves and inflorescences C bracts D corolla.Photo by P. Suksathan.

Table 2 .
Dec 1965gical differences between Strobilanthes phengklaii and similar species.Common in shaded areas in dry evergreen forest; ca.600 m alt., flowering and fruiting from October to December.Etymology.Named in honour of Dr Chamlong Phengklai, a senior botanist at the Forest Herbarium (BKF) who collected the type specimens of S. phengklaii.Phu Luang WS, from Ban Na Luang to north ride ca.600 m alt., 3Dec 1965,  Tagawa et al. 1076 (BKF, KYO, L [L2842098]).

Preliminary conservation status assessment.
This species is only known from its type locality and is assessed as Data Deficient (DD) following IUCN (2022).More field work needed to assess the conservation status of S. phyllocephala.Notes.Strobilanthes phyllocephala resembles S. falconeri.It differs in having the ovate or ovate-elliptic leaves vs. elliptic-lanceolate or lanceolate leaves in S. falconeri.The apex of bracteoles of S. phyllocephala is obtuse vs. acute in S. falconeri.