Thismia thaithongiana Chantanaorr. & Suddee, 2018

Chantanaorrapint, Sahut & Suddee, Somran, 2018, Thismia thaithongiana (Dioscoreaceae: Thismieae), a new species of mycoheterotroph from an unusual habitat, Phytotaxa 333 (2), pp. 287-292 : 287-290

Thismia thaithongiana Chantanaorr. & Suddee , sp. nov. (Figs. 1, 2)

Type:— THAILAND. Tak Province: Umphang District, Doi Hua Mot , 15°58’33.7”N, 98°50’14.4”E, 859 m, 9 Oct 2014, Suddee et al. 4767 (holotype: BKF; isotype: PSU) .

Thismia thaithongiana is mostly similar to T. huangii Jiang & Hsieh (2011: 139) , but differs from the latter in having blue-green flowers, a mitre bearing three horn-like appendages and an arrow-shaped stigma.

Terrestrial, achlorophyllous, mycoheterotrophic herbs. Underground parts clustered, horizontal, vermiform, branched, up to 1.2 mm in diameter, whitish when young, pale brown when old. Stem erect, less than 2 mm long. Leaves glabrous, whitish, scale-like, narrowly triangular to ovate, 1.5–5.0 × 1.2–3.5 mm, apex obtuse to acute; largest leaves just below flower. Involucral bracts 2–3, white, similar to upper leaves. Flowers solitary or paired, opening in succession if the latter, sometimes several clusters on a rhizome, pubescent, blue-green at apex, whitish at base. Perianth actinomorphic with 6 tepals fused to form a perianth tube with mitreform hood. Perianth tube urceolate, 7.5–1.1 × 3.0–8.0 mm, narrowing just above the ovary, widest at the upper third, whitish, sometimes with 12 blue-green vertical streaks in the upper part; inner surface without transverse bars; at the apex with a broad, prominent, blue-green annulus. Outer tepals 3, bluish green, triangular, 1.5–3.0 × 3.0–4.5 wide at base, terminated by horn-like appendages; each appendage 2.0– 4.5 mm long, pubescent. Inner tepals 3, bluish green, connate at the top forming a mitre, with a horn-like appendage developing from the central rib on the outer surface of each; individual horn-like appendage 2.0–4.0 mm long, pubescent; the mitre with three lateral apertures, aperture 2.5–4.5 mm in diameter. Annulus blue-green, 2.5– 3.5 mm in diameter, glabrous. Stamens 6, pendent below mouth of annulus, blue-green at base, creamy-white to pink at apex; filaments glabrous, free, ca. 1 mm long; stamens laterally connate, forming an anther tube; individual stamens spathulate, with 4 thecae (abaxial, dehiscing towards inner surface of perianth tube); theca oblong, ca. 0.8 mm long; nectariferous gland absent; connective of stamens without lateral appendages, not forming a skirt-like appendage; apex of each stamen truncate, hairy. Ovary inferior, cup-shaped, 3.0– 4.5 mm long, pubescent, unilocular, placentas 3; style ca. 1 mm long; stigma trilobed, ca. 1.2 mm long, creamy-white, surface nearly entire; stigma lobes triangular or arrow-shaped, hairy. Mature fruit and seeds not seen.

Figure 1 Thismia thaithongiana . A, B. Plants with flowers. C. Top view of flower. D. Longitudinal section of flower. E. Inner (adaxial) view of three pendulous stamens. F. Stigma and style. All from the holotype (Suddee et al. 4767) by S. Chantanaorrapint.

Figure 2 Thismia thaithongiana . A, B. The type locality, disturbed dry dipterocarp forest on limestone, Doi Hua Mot, Umphang, Thailand. C. Plants in natural habitat. D. Plants with underground parts. E. Immature flower. F. Top view of flower. G, H. Side views of flowers. I. Longitudinal section of flower. A–C & E–I by S. Chantanaorrapint; D. by S. Chanhormhual.

Additional specimens examined:— THAILAND. Tak province: Umphang, Doi Hua Mot , elevation 859 m, 15°58’33.7”N, 98°50’14.4”E, 13 Oct 2012, Srimuang & Chanhormhual s.n. ( PSU) ; same location, 9 Sep 2014, Chanhormhual 01 ( PSU) ; same location, 19 Sep 2014, Chantanaorrapint 2755 ( PSU) .

Distribution:— Endemic to a single mountain in Thailand.

Habitat and Ecology:— Although most of Thismia species are found among leaf litter in shady and moist evergreen forests, Thismia thaithongiana was found in dry dipterocarp forest on a degraded calcareous substrate. The type locality is not close to a stream and is therefore likely to dry out even in the rainy season. The subterranean habit and hairy perianth may protect it from this generally dry environment. It flowers during the late rainy season, September–October.

Etymology:— The epithet honours Assoc. Prof. Dr. Obchant Thaithong, who encouraged the authors to study the genus Thismia .

Conservation status:— Endangered (ENB2 ab (iii,v)) based on a preliminary risk of extinction assessment using the IUCN red list categories and criteria ( IUCN 2012). This species is only known from two localities in the Doi Hua Mot area, 1 km apart on the same mountain. Since there are fewer than 50 individuals at each locality, it is assumed that human activities in these regions could lead them to rapid extinction ( IUCN 2012).

Notes:— Thismia thaithongiana is morphologically similar to T. americana Pfeiffer (1914: 123) from North America and T. huangii Chiang & Hsieh (2011: 139) from Taiwan. The three species share several similarities, viz. vermiform underground parts, short stems, inner perianth lobes forming an erect mitre with three lateral holes, inner surface of perianth tube lacking transverse bars, spathulate stamens without nectariferous glands and annulus form. Thismia americana differs from T. thaithongiana by the outer surface of perianth, stigma lobes and stamens without hairs and a mitre and outer perianth lobes lacking horn-like appendages. It also differs from T. thaithongiana in stigma shape. Thismia thaithongiana , however, is distinguished from T. huangii by the blue-green flowers, a mitre bearing three horn-like appendages and arrow-shaped stigma lobes ( Table 1).