Thunbergia impatienoides ( Acanthaceae ) , a new species from Thailand

A new species, Thunbergia impatienoides, was discovered from Thailand and is here described. Detailed descriptions including pollen and seed morphologies, distribution, ecology and illustration are provided.

The morphological characters of Asian Thunbergia are: Perennial herbaceous or woody climbers, shrubs, rarely erect or trailing herbs without cystoliths.The leaves are always simple and with a petiole, they are opposite, ovate or lanceolate to hastate or sagittate and their margins are entire to lobed to dentate.The flowers are pedicellate, axillary, solitary, paired, up to four arranged in fascicles or with many flowers in racemes with leaf-like bracts.The bracteoles are paired and enclosing the calyx and most or all of the corolla tube, sometimes fused on one side and persistent.The calyx is annular and much shorter than the bracteoles, subentire, undulate or 5 -20-toothed or sinuate.The corolla forms a straight or curved tube.The tube is cylindrical, ventricose or gradually widened towards its apex, ± equally 5-lobed, spreading or recurved and contorted in bud.The stamens are didynamous and inserted near the base of the corolla tube.The anthers are 2-thecous, oblong or ovoid, ± spurred at base, and ± bearded.The disk is short and annular or pulvinate.The ovary is ovoid and consists of 2 locules and has 2 ovules per locule.The style is glabrous or pubescent.The stigma is funnel shaped, bilobed or 2-cleft, and entire or fringed.The fruit is a woody capsule, subglobose at the base and with an elongated beak.Each capsule has 2 -4 seeds which are hemispherical, smooth or sculptured and without retinacula (Imlay 1938, Jiaqi et al. 2011, Adhikari et al. 2013).
While preparing a treatment of Thunbergia for the Flora of Thailand, the beautiful pink flower of this new species attracted our attention.-Fig.1-4; Map 1
Etymology.The specific epithet refers to the gross appearance of its flower which is quite similar to a common ornamental balsam, Impatiens walleriana Hook.f.(Balsaminaceae).
Distribution -Endemic to Thailand (border of northern and western Thailand in Tak province and in western Thailand in Kanchanaburi and Ratchaburi provinces).
Habitat & Ecology -In shaded area in dipterocarp and mixed deciduous forests.Flowering: November to January; fruiting: December to February.Notes -Based on gross morphological characters Thun bergia impatienoides is similar to T. fragrans but differ in having runner stems which is unique.The stem is terete with two furrows (one on each side) and the petiole has a furrow.The flower, which is very showy, is always presented as solitary in the leaf axil.It has an attractive and for Asian Thunbergia unseen pink colour.The distinguishing flower colour characters are dark purple or magenta in flowering bud and turning to pink when mature.The pedicel is rounded and scabrous.The flower is salver-shaped when mature.The corolla lobe is fan-shaped.The five stamens are uniformly didynamous with two shorter and three longer ones.The base of the theca is rounded (usually spurred in Thunbergioideae).The capsule is hirsute and not glabrous and waxy as in T. fragrans (compared in Table 1).The seed of both species are similar but the surface is reticulate in T. impatienoides and long papillate in T. fragrans (Fig. 3).The pollen grains are spheroidal monads.The aperture is spiraperturate which is the common character of Thunbergia.The pollen ornamentation is baculate with fossula.The difference of pollen morphology between T. impatienoides and related species is the size (42-44 ± 0.67 µm vs 54-56 ± 0.68 µm) which significantly supports T. impatienoides to be new to science.The pollen morphological characters of both species are shown (Fig. 4).