Thismia hexagona Dančák, Hroneš, Kobrlová & Sochor, 2013

Dančák, Martin, Hroneš, Michal, Sochor, Michal, Kobrlová, Lucie, Hédl, Radim, Hrázský, Záboj, Vildomcová, Anna, Sukri, Rahayu Sukmaria & Metali, Faizah, 2013, A new species of Thismia (Thismiaceae) from Brunei Darussalam, Borneo, Phytotaxa 125 (1), pp. 33-39 : 34-35

Thismia hexagona Dančák, Hroneš, Kobrlová & Sochor , sp. nov., Fig. 1

Thismia hexagona differs from congeneric species in having the following combination of morphological traits: all perianth lobes equal, tapering into long filiform tentacles, stigmas bifid, yellow hexagonal annulus and four anther appendages.

Type: — BRUNEI DARUSSALAM. Temburong Distr.: Kuala Belalong, eastern ridge of Sungai Belalong, near its confluence with Sungai Temburong. Coordinates WGS 84: N 04° 32.952’; E 115° 09.792’, elevation ca. 320 m a.s.l., 13 February 2013. M. Dančák, M. Hroneš, M. Sochor & L. Kobrlová 2013/17 (holotype BRUN [herbarium specimen, accession number 23947], isotype OL [herbarium specimen, accession number 23093]) .

Terrestrial, achlorophyllous, mycoheterotrophic herb. Roots thick, hardly branched, vermiform, creeping, whitish. Stem erect, simple or poorly branched in upper part, brown, glabrous, 1.7–7.0 cm tall; stem branches usually unequal in length. Leaves few, appressed, scale-like, narrowly triangular, ca. 4 mm long, ca. 2 mm wide at the base, acute at the apex. Floral bracts one or two, similar in shape to the leaves, ca. 7 mm long, ca. 2.0 – 2.5 mm wide at the base. Flowers solitary at the top of each branch. Perianth actinomorphic with 6 tepals fused into urceolate perianth tube with free, equal apical lobes; perianth tube ca. 1.0– 1.5 cm long, pale brownish with lower part usually white, with 12 faint brownish longitudinal streaks and brown-purple apical stripe, widest at the upper quarter, at the apex with broad bright yellow, clearly hexagonal annulus ( Fig. 1B ); inner surface of the perianth tube with 12 faint longitudinal ribs and densely covered with short horizontal bars; perianth lobes brown-yellowish, equally triangular, abruptly ended with long filiform appendages 7–18 mm long, brown-yellowish at the base, white at the top. Stamens 6, borne on thickened margin of the perianth tube; filaments curved downwards, connective broad, connate to form a tube, with two distinct teeth-like appendages at the free apical margins and two thick cylindrical finger-shaped appendages positioned slightly above the marginal ones ( Fig. 1C, D , 2D ). Stigma 3-lobed, lobes shortly bifid ( Fig. 1E ); ovary cup-shaped usually with brown- purple stripe at the top. Fruit cup-shaped brown capsule. Seeds ellipsoid.

Habitat and ecology:— Thismia hexagona grows amongst leaf litter and on rotten logs in the lowland mixed dipterocarp forest. It prefers humid places in gullies formed by small episodic streams ( Fig. 3). A total of 21 flowering individuals were found within the 1-ha permanent forest plot (Plot 1) belonging to Kuala Belalong Field Studies Centre of Universiti Brunei Darussalam ( Hédl et al. 2009).

Distribution:— Species is known only from the type locality: eastern ridge of Sungai Belalong, near its confluence with Sungai Temburong. It is also the first record of the genus and family from Brunei Darussalam (cf. Coode et al. 1996, J. A. Ahmad, pers. comm.).

Conservation status: — The studied population occurs within the designated research zone of Ulu Temburong National Park , to which public access is restricted. The habitat, type locality and its surroundings are thus protected from logging and similar destructive anthropogenic activities. However, it is impossible to assess the current conservation status of this species because there is no information on its population size and dynamics. Therefore, we suggest to evaluate the species as data deficient ( DD) according to the IUCN Red List Categories and Criteria ( IUCN 2012) .

Etymology:— Named after the conspicuous shape of flower annulus.

Variability:—The population as a whole was uniform, with no considerable morphological variation. Most of the individuals were one-flowered, only few two-flowered and one individual with three flowers. Some variability was observed in the colour of the perianth tube. A typical individual had an almost white lower part of the perianth tube, with the upper part brownish and a more or less conspicuous brown-purple stripe at the top just beneath the annulus ( Fig. 2A ). We found two flowering shoots, probably originating from the same root system with a yellow stripe instead of the brown-purple one ( Fig. 2B ), which we suggest is a result of mutation. Few individuals had perianth tubes that were brownish throughout with almost no white basal portion. Most of the plants also had a brown-purple stripe at the top of ovary, which made an impression of two-purple-striped perianth tube.

Figures

FIGURE 1. Thismia hexagona. A. Habit of the plant. B. View of perianth tube mouth with annulus and perianth lobes. C. Connective with anther appendages, side view. D. Apical margin of connective with anther appendages, front view. E. Stigma.

FIGURE 2. Thismia hexagona. A. Plant with typical coloration of perianth tube. B. Plant lacking brown-purple stripe at the top of perianth tube. C. Perianth tube mouth with annulus and perianth lobes. D. Longitudinal section of anther tube with anther appendages.