Thismia inconspicua Sochor & Dančák, 2017

Sochor, Michal, Sukri, Rahayu Sukmaria, Metali, Faizah & Dančák, Martin, 2017, Thismia inconspicua (Thismiaceae), a new mycoheterotrophic species from Borneo, Phytotaxa 295 (3), pp. 263-270 : 264-267

Thismia inconspicua Sochor & Dančák , sp. nov., Fig. 1 .

Thismia inconspicua differs from congeneric species in having the following combination of morphological traits: short stem, all perianth lobes free and equal, tapering into very short terminal appendages, perianth tube displaced from the ovary axis, two pairs of dimorphic appendages on connective apices, three-lobed stigma with lobes entire or bifid.

Type:— BRUNEI DARUSSALAM. Temburong Distr.: Kuala Belalong, a ridge between Temburong and Belalong river valleys ca. 1.4 km SE of their confluence. Coordinates WGS 84: N 04°32’33” ; E 115°09’59”, elevation ca. 280 m a.s.l., 27 January 2016. M. Sochor MS1 /16 (holotype BRUN [accession number B 031 202], isotype OL [accession number 33410]) .

Description:—Terrestrial achlorophyllous mycoheterotrophic herb, 1.6 to ca. 5 cm tall when flowering and to 8.5 cm tall when fruiting ( Figs 1A , 2A–C ). Roots ca. 0.75 mm thick, hardly branched, vermiform, creeping, cream-coloured. Stem erect, ascending, horizontal or almost missing, simple or simply branched, whitish, glabrous, usually less than 1.5 cm (or to 3.8 cm when fruiting) long. Leaves 0–3, appressed, scale-like, same colour as stem, narrowly triangular with acute apex, (2–) 5–8 mm long and ca. 2 mm wide at the base ( Fig. 2E ), margins decurrent and forming long thin lamellae on the stem (stem thus ribbed). Floral bracts two or three, similar to leaves in shape and size, often indistinguishable from them. Flowers solitary. Perianth actinomorphic with 6 tepals fused into an urceolate perianth tube with free, equal apical lobes; perianth tube ca. 7 mm long and 7 mm wide below the apex, (light) brownish with 12 sepia-brown longitudinal ribs, both ribs and background gradually darkening toward the apex; basal part of perianth tube inclined at an angle to the ovary, thus the upper part of the perianth displaced from the ovary axis; Figs 1A , 2A ); inner surface of the perianth tube with 12 longitudinal ribs and faint, pale horizontal bars; apical annulus raised moderately, 4 mm in diameter with opening ca. 2.3 mm wide, sepia-brown on the outer margin, brownish-orange to light orange on the inner margin and grayish in between, inner margin with three shallow notches situated in extensions of the axes of the inner perianth lobes ( Fig. 2B ); perianth lobes sepia-brown, narrowly triangular, 2.5 mm wide at base and 6–6.5 mm long (including 2 mm long terminal appendages arising from the abaxial side of each lobe). Stamens 6, borne on thickened apical margin of the perianth tube; filaments free, short, curved downwards, connectives broad and flattened, laterally connate to form a tube, with two pairs of appendages at the free distal margin – each pair consisting of a club-shaped appendage pointing centripetally and a tooth-shaped appendage pointing centrifugally ( Figs 1D , 2G ); outer side of connective with box-shaped lateral appendage on the distal end protruding towards perianth tube ( Figs 1E , 2F ). Style short, stigma 3-lobed, papillose, lobes longitudinally furrowed ( Figs 1B , 2D ) and sometimes split from the top (then stigmas shallowly to deeply bifid; Fig. 1C ). Capsule cup-shaped, pinkish-brown, on elongated pedicel (to 6 cm long). Seeds beige, ellipsoid, ca. 0.7 × 0.2 mm ( Fig. 2H ).

Variability:—The studied population exhibited very low morphological variability. The most prominent variation was observed for stem length; some plants were almost acaulescent (with leaves and floral bracts forming a single rosette) while the stem of one individual was as long as 3.8 cm. Only small differences were detected in the number of flowers (one or two per individual plant), number of leaves (none to three) and floral bracts (two or three). Due to the limited number of fully developed flowers, variation in generative characters could not be evaluated. Differences in flower coloration, shape of stigma (lobes entire or bifid) and fruit pedicel length (0.5–6 cm) could be ascribed to different developmental stages of each plant and/or plasticity.

Habitat and ecology:—The only known locality of the species is situated in primary lowland mixed Dipterocarp forest in a relatively light gap with a dead standing tree ( Fig. 2I ). Thismia inconspicua grows on decaying fallen branches, lianas and epiphytes, and on organic matter formed after their decomposition. A few individuals were found growing on the lower side of rotten branches. During our study, the locality was still being disturbed by falling limbs and branches, which resulted in slow vegetation restoration. Several other mycoheterotrophic plant taxa were found within 20 m — Epirixanthes elongata Blume (1823: 82) , Tropidia saprophytica Smith (1927: 27) , Gastrodia sp. and Gymnosiphon sp.

Distribution:—The species is known only from the type locality, 0.9 km ESE of the Kuala Belalong Field Studies Centre, Universiti Brunei Darussalam in the Temburong District, Brunei Darussalam.

Conservation status:—The population of T. inconspicua is protected against logging and other anthropogenic disturbance thanks to its location in Ulu Temburong National Park. Despite intensive botanical and ecological research on the locality in the past decades, the species was discovered only recently and by accident. The possibility of its presence being overlooked elsewhere in Brunei or Sarawak thus cannot be precluded due to its inconspicuous appearance and ephemeral growth. Therefore, we suggest evaluating the species provisionally as data deficient ( DD) according to the IUCN Red List Categories and Criteria ( IUCN 2012).

Etymology:—The specific epithet reflects the inconspicuous colour and appearance of the plants on decaying wood during flowering period.

Figures

FIGURE 1. Thismia inconspicua: flowering plant (A), immature capsule with stigma (B), bifid type of stigma (C), longitudinal section of perianth tube (D) and outer view of stamens (E). Drawn by K. Janošíková.

FIGURE 2. Thismia inconspicua: flowering plant (A), plants in different developmental stages (B, C, E), capsule with stigma (D), outer view of stamens (F), appendages on connective apices (G), mature capsule with seeds (H) and the type locality (I).