Thismia nigricans Chantanaorr. & Sridith, 2015

Chantanaorrapint, Sahut & Sridith, Kitichate, 2015, Thismia nigricans Chantanaorr. & Sridith, a new species of Thismiaceae from Southern Thailand, Phytotaxa 217 (3), pp. 293-297 : 294-296

Thismia nigricans Chantanaorr. & Sridith , sp.nov. ( Figs. 1 & 2A–F )

Thismia nigricans is similar to T. angustimitra Chantanaorr. , but differs in having glabrous filaments, the apex of annulus divided into 3 lobes without golden-brown hairs, and the mitre bearing more irregularly dentate ribs.

Type:— THAILAND. Phangnga: Kura Buri, Bang Wan, Sri Phangnga National Park, 08°59’34.06’’ N, 098°27’5.22’’ E, 56 m, 3 August 2014, S. Chantanaorrapint & C. Promma 3897 (holotype, PSU!, isotype, BKF!)

Small terrestrial, achlorophyllous, mycotrophic herbs. Underground parts clustered, creeping, vermiform, branched, brownish-white tip, to 1.5 mm in diameter. Stem erect, simple, whitish, to 11 cm tall, 2.2–2.8 mm in diameter, glabrous, terete. Leaves glabrous, appressed, narrowly triangular with acute apex, scale-like, 2–8.5 mm long, 1.2–2.2 mm wide, leaves increase in size up to the apex of the plant where they are equivalent to floral bracts. Involucral bracts 3, white, similar to upper leaves. Flowers solitary or paired, developing sequentially with only one anthetic. Perianth actinomorphic with 6 tepals fused to form a perianth tube with a foveate mitre. Perianth tube bluish brown or blackish at base, cup-shaped, 5.5–8 mm long, ca 4–8 mm wide, narrowed just above the ovary, widest at the upper third, with 12 irregularly dentate longitudinal ribs, inside with an irregularly reticulate surface without transverse bars. Outer tepals 3, white, ca. 1.7–2 mm long, 3.5–4 mm wide, apex oblique, spreading, rounded or mucronate, margin nearly entire, dorsal surface with 3 irregularly dentate longitudinal ribs. Inner tepals 3, bluish brown or blackish, mitriform with three lateral apertures, aperture 5.5–7 mm in diameter; mitre bearing prominent irregularly dentate ribs and three foveae on top; annulus incurved, ca 5 mm high, glabrous, creamy-white at base, blackish at apex, apex divided into 3 lobes. Stamens 6, creamy-white, pendent below mouth of annulus; filaments glabrous, free, ribbon-shaped, ca. 2 mm long; stamens laterally connate, forming an anther tube; individual stamens with 4 thecae (abaxial, dehiscing towards inner surface of perianth tube), each theca oblong, ca. 1.5 mm long; nectariferous gland present towards apex on the line of fusion between each connective, elliptic-oblong; connective of stamens broad forming a skirt-like appendage, apex of stamens obtuse to round without trichomes. Ovary inferior, obconical, ca. 3 mm long, with papillose longitudinal ridges, unilocular, placentas 3; style short, ca. 0.5 mm; stigmas 3-lobed, ca. 1 mm long, creamy-white, surface papillose, apex of stigma truncate. Fruit cup-shaped, ca. 5 mm long, fruit stalk thickened and lengthened after flowering.

Distribution:—Known only from the type locality in Sri Phangnga National Park, Phangnga Province, Thailand.

Habitat and Ecology:—The type specimens were found growing with other mycotrophic plants such as Epirixanthes sp. and Thismia javanica Smith (1907: 32) , amongst leaf litter, under shade in evergreen forest, ca. 50 m above sea level.

Phenology:—Flowering and fruiting during the rainy season from August to November.

Etymology:—The specific epithet “ nigricans ” refers to the dark color of flowers.

Additional specimen examined:— THAILAND. Phangnga: Kura Buri, Bang Wan, Sri Phangnga National Park, about 200 m to Ton Deng Waterfall, 54 m, 14 November 2012, V. Chamchumroon et al. 5602A (BKF, paratype).

Discussion:— Thismia nigricans is most similar to T. angustimitra Chantanaorrapint (2008: 254) and T. mirabilis Larsen (1965: 171) , both distributed in Thailand. The three species share several similarities in common, viz. reduced outer perianth lobes, the inner ones forming an erect mitre with three lateral holes, the top of the mitre having three foveae, the inner surface of perianth tube possessng an irregularly reticulate surface without transverse bars, and vermiform underground parts. Thismia nigricans , however, is distinguished from T. angustimitra by the absence of golden-brown hairs on the basal part of its stamens and the annulus mouth ( Fig. 2E ). It also differs from T. angustimitra by the mitre bearing more strongly dentate ribs. Thimia mirabilis is separated from T. nigricans by having a broad mitre with smooth surface and erect annulus ( Figs. 2K–M ).

Within the treatment of Jonker (1938), Thismia angustimitra , T. mirabilis , and T. nigricans , resemble the species in sect. Sarcosiphon ( Blume 1850: 65) Jonker (1938: 251) , as they have mitriform flower with three lateral apertures. However, the three species from Thailand differ from the species in sect. Sarcosiphon in having vermiform roots, whilst those in sect. Sarcosiphon have a coralloid root system. Determination of the interrelationships among Thismia species still requires addition of these three species in molecular phylogenetic analyses.

Figures

FIGURE 1. Thismia nigricans Chantanaorr. & Sridith A. Habit. B. Side view of flower. C. Longitudinal section of flower. D. Inner (adaxial) view of three pendulous stamens. E. Stigma. F. Fruit. All from the holotype (PSU, S. Chantanaorrapint & C. Promma 3897) by S. Chantanaorrapint.

FIGURE 2. A–F. Thismia nigricans Chantanaorr. & Sridith: A–B. Habit, C–D. Flowers, E. Longitudinal section of flower, F. Fruit. G–J. T. angustimitra Chantanaorr.: G. Habit, H–I. Longitudinal section of flowers, J. Top view of mitre. K–M. T. mirabilis K. Larsen: K. Habit, L. Longitudinal section of flower, M. Top view of mitre.All photos by S. Chantanaorrapint.