Gomphostemma phetchaburiense Bongch. & Poopath, 2022

Gomphostemma phetchaburiense Bongch. & Poopath View in CoL , sp. nov. — Fig. 1 View Fig , 2 View Fig

This species is recognised by having several stems arising from a woody base growing in limestone crevices, densely dendroid hairs and stellate hairs with a multi-celled stalk on the stems and prominently branching calyx venation. It is morphologically similar to G. velutinum Benth. by having a similar corolla morphology, whitish hairs on stems, and cymes axillary and sessile. Gomphostemma phetchaburiense differs from G. velutinum by having an ascending habit with stout stems (vs sprawling habit with flaccid stems), outer bracteoles longer than the calyx (vs shorter than the calyx), and the calyx tube glabrous inside and constricted at throat with prominent branching veins between teeth (vs pubescent with adpressed simple hairs, not constricted at throat and with unbranched veins). — Type: Poopath et al. 2580 (holo BKF; iso K), Thailand, Phetchaburi Province, Khao Yoi, E-bit Mountain, 60 m alt., 5 Oct. 2020. Paratypes: Poopath et al. 2580 (holo BKF; iso K), Thailand, Phetchaburi Province, Khao Yoi, E-bit Mountain, 60 m alt., 5 Oct.2020; Bongcheewin 1130A (BKF,K, PBM), Thailand, Phetchaburi Province,Khao Yoi,E-bit Mountain, 60 m alt., 14 Nov.2020; Bongcheewin 1130B (BKF), Thailand, Phetchaburi Province, Khao Yoi, E-bit Mountain, 60 m alt.

Etymology. The specific epithet phetchaburiense is derived from the type locality, Phetchaburi Province, southwest Thailand.

Perennial, ascending herbs, 30–50 cm tall. Stems stout, muchbranched from a woody base, obtusely quadrangular, longi- tudinally grooved. Indumentum dense, hairs dendroid and stellate with multi-celled stalks. Leaves chartaceous, densely tomentose with stellate hairs; blades ovate or elliptic, 4–9 by 2.5–3.5(–4) cm, apex acute, base cuneate or sometimes oblique, margin shallowly serrate or incised serrate, lower side pale green; petioles 15–30 mm long. Inflorescence thyrsoid with sessile condensed opposite cymes forming verticillasters, lax with adjacent nodes, 20–40 mm apart, becoming condensed above; cymes 5–7-flowered; bracts subtending cymes leaflike; outer bracteoles sessile, lanceolate or elliptic, 15–20 by 3–7 mm, with dense dendroid hairs on both sides; inner brac- teoles narrowly lanceolate or elliptic-lanceolate, 5–10 mm long, with dense dendroid hairs on both sides. Flowering calyx pale green, infundibular, 8–11 mm long; tube 5–7 mm long, outside with dense, long simple hairs, inside glabrous, constricted at throat due to folding of the base of the sinus and prominent branching veins between teeth; teeth equal, ovate-triangular tapering into the apex, 2–3 mm wide at base, outside densely tomentose with a mixture of long simple and stellate hairs, inside sparsely tomentose with short hairs. Fruiting calyx infundibular, 11–15 mm long; tube 7–8 mm long; teeth equal, triangular, 3–4 mm wide at base, apex subulate. Corolla pinkish white, 25–28 mm long, throat inflated; tube 23–25 mm long, incurved, outside tomentose with short hairs, inside glabrous; upper lip 1-lobed, shorter than lower lip, broadly ovate, apex emarginate, outside sparsely tomentose, inside glabrous; lower lip 3-lobed, pinkish purple; middle lobe tongue-like, margin undulate; lat- eral lobes spreading. Stamens included underneath upper lip; filaments fleshy, white, sparsely tomentose with minute glan- dular hairs; anthers yellowish white. Disc slightly lobed. Style slender, glabrous, shorter than corolla with apex subequally lobed. Nutlets 2 fully developed, narrowly obovate, 3–5 mm long, smooth and glabrous, apex acuminate.

Distribution — Endemic to southwestern Thailand.

Habitat & Ecology — Moist places inside the entrance to limestone caves or growing in rock crevices on the limestone cliff outside with a high degree of exposure to the sunlight; c. 60 m altitude. Flowering & fruiting: October to November.

Vernacularname — Pradapphaphetchaburi(ประดับผาเพชรบุรี, in Thai).

Conservation status — Critically Endangered. Gomphostemma phetchaburiense is known from only one location on a limestone mountain in Phetchaburi Province. Only three clumps of plants were seen around a single cave entrance, c. 20 m high. The mountain is dominated by a colony of hundreds of Rock Pigeons ( Columba livia , family Columbidae ), which invade the habitat of G. phetchaburiense . Furthermore, the bird excrement, which is acidic, may have a detrimental effect to the growth of the new species. There are fewer than 50 mature individuals in a single location, in which is not a protected area. Therefore, we assess the species as Critically Endangered, B2ab(ii,iv,v)+D ( IUCN 2019).

Note — Gomphostemma phetchaburiense shows two forms of leaves, which is seemingly induced by ecological conditions. The leaves with incised serrate leaf margins were found on plants growing in the rock crevices outside the limestone karst ( Fig. 1a View Fig , 2 View Fig ci), those with shallowly serrate leaf margins were found inside the cave entrances or in moister places ( Fig. 1c View Fig , 2 View Fig cii, 2ciii). The climate condition outside the cliff was rather dry due to direct exposure to the sun. The shaded wall of the cave entrance was cooler and more humid. This observation is consistent with the size of leaf teeth being related to the convection coefficient, i.e., the ability of heat to flow through the leaves ( Gottschlich & Smith 1982).