China. Hainan Province: Bawangling, Hainan Tropical Rainforest National Park, in tropical rainforest, 850–950 m elevation, 25 April 2022, Z.Y. Zhang 006 (Holotype, HUFB!).

Gastrodia bawanglingensis is similar to G. albidoides with dwarf habits, scarcely opening flowers, elongated fruit stems, curved and fleshy perianth tubes and similar columns and lips, but can be easily distinguished from the latter by having lateral sepals adnate to 4/5 of total length (vs. lateral sepals adnate to 1/2 of total length), lip with four ridges (vs. lip with two ridges), the absence of a column foot (vs. the presence of a column foot) and a pair of lateral wings bent outwards (vs. lateral wings upright) at the column apex (Table 2).

Figure 4. 

Gastrodia bawanglingensis Z.H.Chen, Z.Y.Zhang & X.Q.Song, sp. nov. A plant B flowers C flattened perianth tube D lip, column and ovary E column F, G lip H fruiting specimen. Illustration by Ling-Yi Cao, based on the holotype of Z.Y. Zhang 006 (HUFB).

Terrestrial, leafless, achlorophyllous herbs. Roots few, slender, 1–7 cm long, ca. 0.5–0.7 mm in diameter. Rhizome fleshy, tuberous, fusiform, 3–4 cm long, 5–7 mm in diameter, dark brown, covered with numerous scales. Scales verticillate, lanceolate, dark brown,1–2 mm long. Inflorescence erect, terminal, 2.0–6.5 cm long, ca. 2.2 mm in diameter, white to orange-brown, peduncle 3–4 noded, ovate to broadly ovate, sheath membranous, 3–5 × 2–3 mm; rachis often less than 5 mm long. Bracts membranous, ovate to ovate-oblong, apex pointed, pale yellowish-brown, 4–6 mm long, 1.5–3 mm wide. Ovary 3–6 mm long, 2–3 mm in diameter. Flowers (1–) 2–4 (–6), erect, bell-shaped, slightly curved, not opening widely, 8–10 mm long, 4–5 mm in diameter. Flowers whitish on both surfaces, apex brownish, lip red at the base, light green at the middle, reddish-brown apically and marginally; column white. Sepals and petals united, forming a 5–lobed perianth tube, 8–10 mm long, slightly verrucous in the middle and upper part, distinctly verrucose apically. Sepals fleshy, thickened, similar. Lateral sepals fused to 4/5 of their length, whitish on both surfaces, apex is brownish; free lobe of dorsal sepal triangle, ca. 2.5 × 2.0 mm; free lobes of lateral sepals ovate, ca. 2.0 × 2.0 mm. Petals connate with sepals, free portions brownish, whitish on both sides, triangular-ovate, ca. 1.5 mm long, 1 mm wide, connate portions distinctly thickened and the inside is obviously reddish-brown, forming a pair of ridge-like structures inside the perianth tube and the other side of the ridge-like structures is flesh-coloured. Lip rhombic-ovate, base adnate to perianth tube, 3.5–4.5 × 2.0–2.2 mm; hypochile with two whitish, globose, subsessile, nectarless calli, ca. 0.5 mm in diameter; epichile 5–7 nerved, truncate at base, entire, disc thickened with four ridges, a pair of low ridges outside the two main ridges; the two main ridges fused into one before reaching the tip, main ridges much raised and tinged orange near apex. Column 4.2–4.5 × 1.6–1.8 mm, apex with a pair of lateral wings bent outwards; lateral wings with acuminate tips lower than anther; column foot absent; rostellum 0.2 × 1 mm; stigma located near base. Anther hemispherical, 0.6–0.7 mm in diameter; pollinia 2. Capsule ellipsoid, 1.2–1.8 cm long, 0.5–0.8 cm in diameter; pedicel elongating to 10–25 cm in fruit. Seeds fusiform, 1.6–2.2 mm long.

The new species is named after Bawangling, the mid-west State of Hainan Island where it was discovered in a vast area of primitive montane rainforest.

霸王岭天麻 (Chinese pinyin: bà wáng lǐng tiān má).

Gastrodia bawanglingensis is a terrestrial mycoheterotrophic species that grows in montane rainforests which are dominated by Dysoxylum gotadhora (Buch.-Ham.) Mabb., Livistona saribus (Lour.) Merr. and A.Chev., Hancea hookeriana Seem. and Engelhardia roxburghiana Lindl. at elevations from 850 m to 950 m and associated with other orchids, such as Anoectochilus hainanensis H.Z.Tian, F.W.Xing & L.Li, A. roxburghii (Wall.) Lindl., Oxystophyllum changjiangense (S.J.Cheng & C.Z.Tang) M.A.Clem., Dendrobium hainanense Rolfe, Cymbidium kanran Makino and Micropera poilanei (Guillaumin) Garay. So far, only the type subpopulation has been found in the tropical rainforest of Bawangling, in Hainan.

Endangered [EN D1]. Gastrodia bawanglingensis was discovered in the mountain rainforest of Bawangling in Hainan Tropical Rainforest National Park. Until now, only the type subpopulation, consisting of ca. 100 individuals, has been discovered in Bawangling. Since its number of mature individuals is fewer than 250, we assess it as Endangered (EN) using criterion D1 (IUCN Standards and Petitions Subcommittee 2022).

Gastrodia bawanglingensis was observed flowering and fruiting in April and May.

Flowers of Gastrodia bawanglingensis barely open and pollen massulae were observed on the stigma when flowers were dissected. Through field observation, it was found that the fruiting rate is very high. We bagged buds on 3 plants with 10 flowers in total prior to the anthesis, and found that each of them has evolved into fruit after 15 days. These observations indicate that the new species probably self-pollinates. Gastrodia is probably the only genus that contains species with completely cleistogamous flowers as confirmed by intensive monitoring. Self-pollination might be an adaptation to ensure reproduction, compensating for the defi- ciency of pollinators in the habitat (Suetsugu 2022; Suetsugu et al. 2022). Currently, complete cleistogamy has been reported in five Gastrodia species: G. clausa, G. takeshimensis, G. flexistyloides, G. kuroshimensis and G. amamiana (Hsu et al. 2012; Suetsugu 2013, 2014, 2016, 2019), G. bawanglingensis is likely to be the sixth species reported. Similar to other five species, G. bawanglingensis is also distributed on the island, further confirming island colonization may be one of the factors of evolution of complete cleistogamy. And compared with the mainland, there are more frequent geological and climate changes on the island, which may cause the rapid change of its living environment and lead to the loss of pollinators in its distribution area. Unreliable pollinator services and the cost of maintaining open flowers probably drove the completely cleistogamous Gastrodia species to abandon insect-mediated pollination (Suetsugu 2014, 2016). However, complete cleistogamy has arguably driven speciation (Kishikawa et al. 2019; Ogaki et al. 2019). We also found several other unpublished species that are different but very similar to G. bawanglingensis in our field survey in Hainan Island, which also confirms the above point of view. It is also notable that although lack of rostellum often facilitates selfing in the genus (Suetsugu 2022; Suetsugu et al. 2022), the new species has somewhat well-developed rostellum. Further observations are needed on how the species accomplishes autogamy.