﻿A taxonomic synopsis of Heliotropiaceae and new combinations in Heliotropium from Thailand

﻿Abstract A synopsis of Heliotropiaceae in Thailand is presented and, as part of this, the taxonomic history, identification keys, distribution maps, herbarium specimen citations and diagnostic characters are provided. Two genera and 12 species are recognised and four new combinations are proposed of Tournefortia under the genus Heliotropium, namely H.hookeri, H.intonsum, H.montanum and H.ovatum. Two species are newly recorded in Thailand: Euplocaovalifolia and H.hookeri. The neotype and lectotype are designated here for Tournefortiamontana and T.boniana, respectively.

In Southeast (SE) Asia, the contributions to the knowledge of Tournefortia and Heliotropium remain controversial.Many traditional Tournefortia species were recognised by Gagnepain and Courchet (1914), Ridley (1923), Johnston (1935), Backer and Bakhuizen van den Brink Jr (1965), Zhu et al. (1995) and Riedl (1997).Fletcher and Kerr (1951) reported the first checklist of the Heliotropiaceae species in the Florae Siamensis Enumeratio.The present study aims to: 1) provide a synoptic account of Heliotropiaceae for the Flora of Thailand, 2) present an identification key for species recognition and 3) propose new combinations of Tournefortia into Heliotropium.

Materials and methods
Extensive collections of herbarium specimens at AAU, ABD, BK, BKF, BM, C, CMU, CMUB, E, K, K-W, KKU, L, QBG and SING (abbreviations follow Thiers 2022, continuously updated) were studied together with living material observations in the field.Species delimitation was based on the examination of original publications including the relevant literature: Clarke (1885); Gagnepain and Courchet (1914); Ridley (1923); Johnston (1935Johnston ( , 1951)); Backer and Bakhuizen van den Brink Jr (1965); Zhu et al. (1995); Riedl (1997);Mill (1999).The type collections were observed online in JSTOR Global Plants (https://plants.jstor.org/).Most measurements were taken from dried specimens and spirit-preserved material and colour descriptions were studied from living material.Distribution, ecology and flowering and fruiting data were derived from specimen labels.All specimens were imported into Sim-pleMappr (Shorthouse 2010) to create distribution maps.All collections cited that have been seen by the authors are marked with '!' and those seen as digital images are indicated with 'image'.
The molecular data and morphological species concept (Hilger and Diane 2003;Diane et al. 2016;Luebert et al. 2016) were used in the present study.This concept is consistent with that of previous studies (i.e. de Candolle (1845); Gagnepain and Courchet (1914); Johnston (1935Johnston ( , 1951)); Fletcher and Kerr (1951); Förther (1998)).Particular morphological features that were employed to delimit species in Euploca species are: stem position and branching, the presence of bracts in the inflorescence, cyme type and floral and fruit structure.For Heliotropium, features used include: habit, the presence of bracts in the inflorescence, cyme type and floral and fruit structures.For the generic circumscription, both morphological and molecular data are considered (Diane et al. 2002;Hilger and Diane 2003;Luebert et al. 2016).Morphologically, Euploca is separated from Heliotropium due to the bracteate inflorescence and fruit breaking up into four distinct nutlets.The terminology used in this present study is adapted from Weberling (1992) and Beentje (2012).Description.Annual or perennial herbs, climbing shrubs or small trees.Leaves simple, alternate, exstipulate, petiolate or sessile; lamina linear to ovate, apex acute to acuminate, margin entire or revolute.Inflorescences terminal or axillary, spike-like, scorpioid, subcapitate or subcorymbose cymes; with or without bracts.Flowers 5-merous, rarely 4-merous, bisexual, actinomorphic.Calyx 5-lobed, divided almost to the base, lobes linear to ovate, entire, persistent.Corolla white to pinkish-white, purple, pale green or greenish to yellowish, campanulate to funnel-shaped, lobes orbicular.Stamens 5, filaments adnate to the corolla tube.Pistil ovary superior, bicarpellate, usually 4-loculate, 1 ovule per locule, nectar disc at the base surrounds the ovary; style terminal, with a conical stigma structure forming a basal ring around style.Fruit dry or fleshy, separating into four 1-seeded nutlets or two 2-seeded nutlets.Seeds straight or curved, with endosperm.

Key to the genera of Heliotropiaceae in Thailand
Ecology.Open areas in deciduous forest, dry secondary forest; 50-300 m alt., flowering and fruiting from February to October.Diagnostic characters.Euploca bracteata is suberect, with sparsely white pubescent hairs on both leaf surfaces, subcapitate cyme inflorescence at the end of branches and sessile flower or with pedicels up to 1 mm long.This species is similar to E. marifolia, sharing a similar habit, flowers and inflorescence form, but differs in having elliptic leaves (vs.linear to lanceolate leaves in E. marifolia).Type.Based on Heliotropium marifolium J.Köenig ex Retz.Distribution.Pakistan, India, Sri Lanka, China, Cambodia, Vietnam, Thailand (Fig. 1B), Peninsular Malaysia, Java.
Ecology.Open area, sandy soil on riverbanks, rice fields, grassland, along roadsides; ca.200 m alt., flowering and fruiting from December to May.Diagnostic characters.Euploca ovalifolia is newly recorded for Thailand.It is recognised by elliptic to obovate or oblanceolate leaves with silky silver hairs, spike-like or scorpioid cymes inflorescence with pedicels up to 2 cm long and a white corolla with a yellowish to yellow centre.This species is similar to Heliotropium indicum in its inflorescence form, but differs in its leaf shape, bracteate inflorescences (vs.ebracteate in H. indicum) and fruit breaking up into four nutlets (vs.breaking up into two nutlets in H. indicum).Diagnostic characters.Euploca paniculata is erect with unbranched to fewbranched stems that are woody at the base.The distinguishing features are linear leaves with greyish tomentose hairs, the spike-like inflorescences arranged in one rank that can elongate up to 20 cm and flowers with pedicels up to 2 mm long.The herbarium specimens from Thailand have mostly been confused with E. strigosa, but these two species can be differentiated by leaf shape and type of induments that are greyish tomentose (E.paniculata) and strigose (E.strigosa) on both leaf surfaces.Diagnostic characters.Euploca strigosa is most similar to E. paniculata in having spike-like inflorescences arranged in one rank that can elongate up to 10 cm long, but it differs in the stem being a prostrate to many-branched (vs.erect unbranched to few-branched stem in E. paniculata), the narrowly elliptic leaves with strigose hairs on both surfaces, 5-10 × ca. 3 mm (vs.linear leaves with greyish tomentose hairs, 7-40 × 1-2 mm in E. paniculata).Mallotonia gnaphalodes (L.) Britton.
Ecology.Sandy beaches, flowering and fruiting from November to February.
Vernacular.Ya nguang chang (หญ้ างวงช้ าง).Diagnostic characters.Heliotropium indicum is likely native to tropical America and introduced in all the tropical regions of the world.This species is also a common weed with medicinal properties (Dash and Abdullah 2013).It is most easily recognised by ovate to elliptic leaves with strigose and stiff hairs on both surfaces, truncate or obtuse leaf base, irregularly undulate leaf margins, white to purple or purplish corollas with a yellow-orange throat inside and fruits are deeply 2-lobed with apical divergent lobes.Diagnostic characters.Heliotropium intonsum is most similar to H. montanum in its dichotomous branched inflorescences and subsessile pedicels, but differs in the leaves being oblong or elliptic with densely strigose hairs (vs.glabrous to glabrescent ovate-lanceolate leaves in H. montanum) and both the inflorescences and corollas bear densely greyish tomentose hairs (vs.glabrous in H. montanum).Distribution.India (Assam), Bangladesh, southern China, Myanmar, Laos, Vietnam, Cambodia, Thailand (Fig. 1K).

Heliotropium
Ecology.Open roadside, along the streams in evergreen forest, bamboo forest, slopes of the hills in evergreen forest and mixed deciduous forests, 250-1,500 m alt., flowering and fruiting from February to December.
Specimens examined.Diagnostic characters.Heliotropium montanum can be recognised by ovate-lanceolate leaves, glabrous to glabrescent on both surfaces and minute tubercules on the lower surface, loosely dichotomous branched inflorescences and glabrous flowers.The specimens from Thailand have mostly been misidentified as H. intonsum.These two species can be differentiated by leaf shape, the type of indument on each of the inflorescences and corollas that are glabrous (H.montanum) or densely greyish tomentose hairs (H.intonsum).
In the original description of T. montana Loureiro (1790) described from 'Cochinchina tributarii', the type collection of Loureior has not been found in either P or BM.Therefore, this species is represented by specimens of Gaudichaud 180 (K000998140, P03897604, P03897602) from 'Cochinchine: Tourane', Loureiro's initial locality.The specimen at P [P03897604] is designated here as a neotype for T. montana because it is in the best condition and the characters match the original description.
In the protologue, Gagnepain (1914) described T. boniana, based on two different collections (Bon 1357& Bon 1932). Bon 1932 P [P03897617] is chosen as the lectotype because it is best preserved, with complete inflorescences and numerous flowers and has two duplicates.Gagnepain (1914) did not specify which of the duplicates of T. gaudichaudii was the holotype; therefore, the specimen at P [P03897604] is designated as the lectotype because it is a perfect match for the description in the protologue.Distribution.India (Andaman Islands, Nicobar Islands), Myanmar, Thailand (Fig. 1L).
Ecology.Open or shaded, slightly disturbed area in mixed evergreen forest 400-500 m alt., flowering and fruiting from November to April.Vernacular.Liang (เหลี ยง).Diagnostic characters.Heliotropium ovatum is similar to H. biblianum in having ovate or ovate-lanceolate leaves, but differs in the 5-merous flower and densely minute tubercules on the lower leaf when dry (vs.4-merous flowers and minute tubercules on both leaf surfaces in H. biblianum).

Figure 1 .
Figure 1.Distribution of Heliotropiaceae from Thailand, based on the specimens examined.

Figure 3 .
Figure 3. Species of Euploca from Thailand A-C E. paniculata (R.Br.)M.W.Frohl.& M.W.Chase A habit and inflorescences B inflorescence C young fruits D-F E. strigosa (Willd.)Diane & Hilger D inflorescence E habit F habit and inflorescences.Photos by Kanokorn Rueangsawang.

Figure 4 .
Figure 4. Species of Heliotropium from Thailand A-C H. foertherianum Diane & Hilger A inflorescence B habit C flowers D-F H. indicum L. D inflorescences E habit and inflorescence F young fruits.Photos by Kanokorn Rueangsawang.