Gastrodia damingshanensis A.Q. Hu & T.C. Hsu, 2014

Hu, Ai-Qun, Hsu, Tian-Chuan & Liu, Yan, 2014, Gastrodia damingshanensis (Orchidaceae: Epidendroideae): a new mycoheterotrophic orchid from China, Phytotaxa 175 (5), pp. 256-262 : 256-261

Gastrodia damingshanensis A.Q. Hu & T.C. Hsu , sp. nov. ( Fig. 1–3 )

This new species is close to G. uraiensis T.C. Hsu & C.M. Kuo and to G. fontinalis T.P. Lin , but can be distinguished by its longer inflorescence, the short column hidden under the lip, without well-developed column wings and rostellum, and the reddish brown, rhombic-elliptic lip with a retuse apex.

Type:— CHINA. Guangxi: Nanning, Damingshan National Nature Reserve , evergreen broad-leaved monsoon forest, by the roadside, 1100–1200 m, 31 March 2013, T. C . Hsu & A. Q . Hu 6407 (holotype: TAIF!; isotype: IBK!) .

Terrestrial, leafless, achlorophyllous herbs. Roots few, slender, extending from apex of rhizome. Rhizome tuberous, fusiform, 40–70 mm long, 5–8 mm in diameter, grayish brown, covered with verticillate, lanceolate scales and finely unicellular hairs. Inflorescence erect, terminal, 1–2(–3)-flowered, 9–25 cm long, ca. 2 mm in diameter, glabrous, grayish brown; peduncle 7–23 cm long, with 3–4 sterile bracts; sterile bracts sheathing, membranous, ovate to broadly ovate, 4.5–10.0 mm; rachis up to 2 cm long. Bracts membranous, glabrous, ovate to ovate-oblong, apex acute, 3.0–4.0 × 2.0– 2.5 mm. Pedicel and ovary 7–10 mm long, pedicel slightly curved, ovary 2.0– 3.5 mm in diameter, slightly verruculose. Flowers nodding, bell-shaped, not widely opening, dark yellowish brown. Perianth tube 11–15 mm long, 5-lobed, distinctly verruculose abaxially. Sepals fleshy, 11–15 mm long, fused for 1/2 length with each other and for 2/3 with petals, glabrous and grayish brown adaxially; free part of dorsal sepal straight, ovate, 4.0–5.0 × 4.0– 4.5 mm, apex obtuse, slightly concave; free parts of lateral sepals slightly spreading, oblique ovate-triangular, 4.5–5.5 × 5.0–6.0 mm, entire, apices apiculate, midribs prominently ridged abaxially and slightly elevated adaxially. Free parts of petals ovate-orbicular, 3.0–3.5 × 3.0– 3.5 mm, entire, apex obtuse-rounded, base slightly clawed. Lip adnate to distal part of column-foot, free from perianth tube, entire, fleshy, 7–8 × 4–5 mm; hypochile pale yellowish brown, with two dark yellow-green, globose, sessile, nectarless calli; epichile rhombic-elliptic, reddish brown, apex retuse, disc with 4–6 longitudinal ridges, the central two much longer and prominent. Column stout, compressed, obscured by the lip bent over it and therefore invisible from the entrance of perianth tube, 2.0–2.5 × ca. 2.0 mm, white tinged with reddish brown at base; column-foot well developed; column wing absent; rostellum not prominent; stigma convex, ca. 1.8 × 1.8 mm; anther adpressed to stigma, incumbent, hemispheric, two-locular, ca. 1.1 × 1.5 mm, anther cap abaxially ridged; pollinia 2, whitish, sectile; caudicles absent.

Additional specimens examined:— CHINA. Guangxi: Nanning, Damingshan National Nature Reserve , 1100– 1200 m, 31 March 2013, T. C . Hsu & A. Q . Hu 6425 ( TAIF!, IBK!) .

Distribution and habitat:— Gastrodia damingshanensis is so far only known within the Damingshan National Nature Reserve, Guangxi. In addition to the population at the type locality, four more subpopulations were found scattered in forest in other parts of the nature reserve between 1,100 and 1,200 m elevation. Population sizes were generally small, ranging from 5 to 20 emergent individuals at the time of observation. All five populations share a common habitat, namely evergreen broad-leaved monsoon forest. Growing in semi-shade in thick, damp grey-brown humus, it’s difficult to spot this inconspicuous leafless orchid in the understorey.

Phenology:— Gastrodia damingshanensis flowers from late March to April.

Etymology:— The specific epithet was chosen in reference to the type locality, Damingshan National Nature Reserve in Guangxi, China.

Taxonomic remarks:— Morphologically, Gastrodia damingshanens is most similar to G. uraiensis Hsu & Kuo (2010: 244) and G. fontinalis Lin (1987: 129) from Taiwan by sharing a few-flowered inflorescence, a bell-shaped perianth tube, and a lip with several longitudinal ridges. However, it is not difficult to distinguish G. damingshanensis from the other two because of its longer peduncle, the compressed column hidden by the lip, and the different lip shape and coloration. Detailed comparisons between the three species are made in Table 1.

Pollination Biology:—Dissections of fresh flowers revealed that the anther and pollinia of Gastrodia damingshanensis are in direct contact with the stigma because of the strongly incumbent column apex. Hence, we predict that this new species is obligatory self-pollinated. Such a specialized column structure is unusual but not unique in the genus Gastrodia , since similar cases are found in G. minor Petrie (1893: 273) and G. cunninghamii Hooker (1852: 251) from New Zealand, which are also regarded as self-pollinated ( Hatch 1949, 1954; Molloy 1990). This unusual structure seems to be a result of convergent evolution among G. damingshanensis and the two New Zealand species as suggested by the dissimilarity of other vegetative and floral characters and very distant geographic distribution.Aphids were observed living inside the flowers of G. damingshanensis , damaging perianth tubes in three of the five reported populations. Lehnebach et al. (2005) also reported aphids visiting G. cunninghamii in New Zealand. However, the status of these aphids as efficient pollinators is doubtful and they may not contribute to the high natural fruit-set of G. cunninghamii (up to 92%). There are several other Gastrodia species documented to show morphological and functional adaptions to promote self-pollination, such as the absence of a prominent rostellum (referring to median stigma lobe, the concept of which follows Dressler (1993) in G. albida Hsu & Kuo (2011: 272) , G. appendiculata Leou & Chung (1991: 138) , G. clausa Hsu, Chung & Kuo (2012: 271) , G. confusoides Hsu, Chung & Kuo (2012: 273) and G. theana Averyanov (2005: 90 ; Hsieh et al. 2012), a strongly incurved column in G. flexistyla Hsu & Kuo (2010: 243) leading the anther to its direct contact with the stigma ( Hsu & Kuo 2010), and cleistogamy in G. peichatieniana Ying (1987: 690) and G. clausa . Several factors may contribute to these evolutionary transitions, such as resource limitation of myco-heterotrophic plants and comparatively short above-ground life cycle, which at the same time leads to the shortage of sufficient pollinators. It would be intriguing to test the hypotheses of morphological adaptations to harsh environment and resource constraints in these myco-heterotrophic orchids.

Figures

FIGURE 1. Habitat and habit of Gastrodia damingshanensis A.Q. Hu & T.C. Hsu (at the type locality). Photographed by T.C. Hsu.

FIGURE 2. Gastrodia damingshanensis A.Q. Hu & T.C. Hsu (drawing based on T. C. Hsu & A. Q. Hu 6407). A. Habit. B–E. Flower (B. Top view, C. Bottom view, D. Longitudinal section, E. Frontal view). F. Perianth tube, expanded and flattened. G. Lip and column, side view. H. Lip. I–J. Column (I. Front view, J. Back view). K–L. Anther cap (K. Top view, L. Bottom view). M. Pollinia. Illustrated by T.C. Hsu.

FIGURE 3. Gastrodia damingshanensis A.Q. Hu & T.C. Hsu (Plate based on T.C. Hsu & A.Q. Hu 6407). A. Habit. B–E. Flower (B. Top view, C. Side view, D. Bottom view, E. Frontal view). F. Perianth tube, expanded and flattened. G. Lip and column, side view. H. Column with anther attached, side view. I–K. Column without anther (I. Back view, J. Front view, showing melted pollinia on stigma, K. side view). L–M. Lip. N–O. Anther cap (N. top view, O. bottom view). P. Pollinia. Photographed by T.C. Hsu.