Thismia puberula (Thismiaceae), a new species from Southern Vietnam

Thismia puberula Nuraliev

Thismia puberula differs from related T. angustimitra Chantanaorrapint (2008: 524), T. mirabilis K. Larsen (1965: 171), T. mucronata Nuraliev in Nuraliev et al. (2014: 246) and T. okhaensis Luu, Tich, G.Tran & Q.D.Dinh in Truong et al. (2014: 190) by the domeshaped annulus with delimited vertical and horizontal parts and by the annulus outer surface covered by hairs. This species also differs in the following combination of morphological traits: flower short (1.9 cm long), mitre broader than hypanthium, mitre outer surface with foveae, mitre inner surface covered by papillate trichomes, base of filament occupying the entire height of the inner surface of the annulus, and the presence of interstaminal glands.

Type

VIETNAM. Dak Lak province: Lak district, Bong Krang municipality, Chu Yang Sin national park, 12 km S from Krong Kmar village, in the forest, on an islet of a small river, elevation ca. 1100 m a.s.l., N 12° 23’ 41’’, E 108° 20’ 55’’, 28 May 2014, Nuraliev 1000 (holotype MW!, stored in ethanol).

Etymology

The specific epithet “puberula” means “covered by short hairs” and refers to the presence and nature of the annulus indumentum which differs this species from the most similar ones T. angustimitra, T. mirabilis, T. mucronata and T. okhaensis.

Distribution and habitat

Currently only known from Dak Lak province in Southern Vietnam. The type specimen is represented by a single plant, and despite our intensive search around the area of this collection no more individuals were discovered.

Phenology

The plant observed in late May possessed a single flower which was in anthetic condition. Besides, a small lateral bud was found in the axil of one of the involucral bracts. It is highly possible that one or more successively blooming flowers develop after the first one, forming a cincinnus, as is known for many other species of Thismia (Stone 1980, Larsen 1987, Maas-Van de Kamer 1998, Larsen & Averyanov 2007, Ho et al. 2009, Tsukaya et al. 2014, Mar & Saunders 2015). We therefore suppose that our collection was made at the very beginning of the flowering season of T. puberula. Such an assumption is also consistent with the observed rarity of this species, as other individuals could probably stay with above-ground shoots not yet fully developed at this time of year and thus could not be spotted.

Flower and fruit biology

Representatives of the genus Thismia are commonly believed to be pollinated by small flies, and recent direct observations are in concordance with this viewpoint (see Mar & Saunders 2015 and references therein). Flower structure of T. puberula is also consistent with this presumed mode of pollination. Interstaminal glands, when present, are frequently described as nectariferous (e.g. Saunders 1996, Thiele & Jordan 2002, Chantanaorrapint & Sridith 2007, Chantanaorrapint 2008, 2012, Chantanaorrapint & Chantanaorrapint 2009, Chiang & Hsieh 2011, Tsukaya & Okada 2012, see also discussion by Mar & Saunders 2015). However, no nectar secretion was detected in T. puberula (our observations) as well as in T. angustimitra and T. mirabilis (S. Chantanaorrapint, pers. comm.). On the other hand, it should be taken into account that examination of the glands is impossible without damage to flower structure, which makes the continuous observations problematic, while the presence of nectar should be checked at various times of the day and different phenological stages.