Thunbergia kasajuana, a new species of Acanthaceae from Nepal

A new species of Thunbergia, T. kasajuana Bh.Adhikari & J.R.I.Wood is described from central Nepal. It is most closely related to T. grandiflora Roxb., because of its reduced annular calyx and similar inflorescence structure but differs in the much smaller corolla, herbaceous habit and different ecology. A description, photographs and a key to the species of Thunbergia native to Nepal are provided.


Introduction
The genus Thunbergia Retz. comprises around 100 -150 species (Borg et al. 2008;Vollesen 2008;Mabberley 2017) distributed through the tropical and subtropical regions of the Old World. It consists of erect or twining plants, although the native species of the Himalayas are all twiners. It is characterised by the presence of two large bracteoles enclosing the calyx and part of corolla tube, the reduced annular rim-like or shortly toothed calyx, and a woody capsule with a prominent beak. Several species are cultivated in tropical and temperate regions of the world because of their showy flowers, including T. laurifolia Lindl., which appears to be closely related to T. grandiflora Roxb. but is so far unrecorded from Nepal, T. alata Bojer ex Sims and T. erecta (Benth.) T. Anderson, both of which are known to be cultivated in Nepal. The only native species cultivated as an ornamental is T. coccinea Wall. ex D.Don.
The main centre of diversity of the genus is south and east Africa, 49 species being recorded in the Flora of Tropical East Africa (Vollesen 2008). It is less diverse in Asia with around 35 species recorded from SE Asia (Bremekamp 1955), 13 species (10 native) from India (Karthikeyan et al. 2009), six from China (Hu et al. 2011), five from Bhutan (Wood 2001) and 14 from Myanmar (Kress et al. 2003) of which 11 are native.
The five recognised native species from Nepal were described, discussed and illustrated by Adhikari et al. (2013). The commonest species is the very distinctive red-flowered Thunbergia coccinea (Fig. 1F) which is widely distributed in tropical and subtropical forest from 100 -2100 m throughout Nepal. Thunbergia fragrans Roxb. (Fig. 1A, B), and T. grandiflora (Fig. 1D, E) are both commonly found in Tarai forest, and on the lower slopes of the Himalayas in central and eastern Nepal. Thunbergia lutea T.Anderson is rare and known from only two localities in eastern Nepal but is easily distinguished from other species found in Nepal by its pinnately veined leaves. Thunbergia nepalensis Bh.Adhikari & J.R.I.Wood (Fig. 1C) is found at around 2100 m in two locations in western Nepal and is distinguished by its 5 -7-toothed calyx, the teeth ovate-deltoid in shape. The discovery of T. kasajuana Bh.Adhikari & J.R.I.Wood by Saroj Kasaju in the Nagarkot region of central Nepal brings the total number of native Thunbergia species known from Nepal to six.
The most recent infrageneric classification of the genus by Bremekamp (1955) recognised seven subgenera to which one was added by Vollesen (2008). These subgenera are partially supported by molecular studies (Borg et al. 2008). The new species appears to belong to subgen. Hexacentris Benth. & Hook.f. emend. Bremek. to which T. grandifolia and T. coccinea also belong. It is a monophyletic, "rather well-defined group of woody climbers" (Borg et al. 2008) which can be recognised morphologically by its annular calyx and eglandular corolla.

Materials and Methods
This paper is based on field studies by the first author in Nepal and by studies of specimens and literature by both authors. Specimens of Thunbergia, including the types, were examined at BM, E, K and KATH herbaria (herbarium codes follow Thiers, 2016 onwards). Published literature on the genus Thunbergia (Bremekamp 1955;Wood 2001;Vollesen 2008;Karthikeyan et al. 2009;Hu et al. 2011;Adhikari et al. 2013) was also checked. The specimens and photographs of the new species were compared with all known species of Thunbergia from adjacent regions. Particular attention was paid to species recorded from north east India and Myanmar, those from South India pertaining to a different phytogeographical region. Of those listed by Karthikeyan et al. 2009, only two from northern India were unknown in Nepal and both of these, T. leavis Nees and T. maculata Lace were clearly related to T. fragrans and thus belonged to a different subgenus of Thunbergia. Search through the Myanmar checklist (Kress et al. 2003) revealed two possible species said by their authors (Gamble 1913;W. W. Smith 2014) to belong to subgen. Hexacentris, although both were recorded far to the east of Nepal. Both are represented in the Kew herbarium; T. lacei Gamble has a dentate calyx so can be excluded from consideration; T. papilionacea W.W.Sm. appears to be correctly placed in subgen. Hexacentris but differs from T. kasajuana in its subtomentose indumentum, densely hirsute ovary and presumed purple flowers.
The following key is a modified version of that provided by Adhikari et al. (2013) with the addition of the new species.
Bhaktapur district of Central Nepal. More extensive collections from similar habitats from subtropical and temperate regions of Nepal will be needed to confirm its conservation status but the forest where it is found is reported to be still in good condition. Saroj Kasaju also reports having seen it on Shivapuri Hill near Kathmandu, but no specimens have been seen. It is accordingly categorised as Data Deficient according to the IUCN Red List of Threatened Species (IUCN 2012), until more information about its distribution and the status of its population becomes available.
PHENOLOGY. This species flowers in August and September at the end of the wet monsoon season and has been found in fruit in September and December. ETYMOLOGY. The specific epithet kasajuana honours Mr Saroj Kumar Kasaju, who first discovered and photographed the species. Mr Kasaju is a citizen scientist contributing to our understanding of the flora of Nepal by taking photos of plant species from Nepal and India. He was actively involved in the identification of this species.