Adelopetalum howense D.L.Jones, M.A.Clem. & H.Zimmer, 2024

Jones, David L., Zimmer, Heidi C., Clements, Marka., Bruhl, Jeremy J., Christian, Joel, Copeland, Lachlan M., Hutton, Ian, Andersen, Alexandra & Wilson, Melinda, 2024, Characterisation of Adelopetalum argyropus (Orchidaceae; Malaxideae) with the description of two related new species and two new combinations, Phytotaxa 678 (1), pp. 83-95 : 90-93

Adelopetalum howense D.L.Jones, M.A.Clem. & H.Zimmer , sp. nov. ( Fig 5 )

TYPE:— AUSTRALIA . New South Wales, Lord Howe Island, 20 May 2001, Hutton 830 (holotype: NSW494145).

Adelopetalum howense is similar to Adelopetalum argyropus but differs by its broadly oblong to broadly elliptical pseudobulbs with a flat to shallowly conical apex (globose to obconical or turbinate pseudobulbs in A. argyropus , the apex with shallow to deep depressions); flowers pendent, opening widely (flowers porrect to weakly decurved in A. argyropus , not opening widely); lateral sepals widely divergent, cream to pale yellow with a contrasting protruding deeply orange labellum (lateral sepals weakly divergent, cream to greenish yellow, labellum not longer than sepals). From Adelopetalum continentale , it differs from in its broadly oblong to elliptical pseudobulbs with a flat to shallowly conical apex (ovoid to conical or transversely elliptic pseudobulbs with a flat apex in A. continentale ), pendent flowers (porrect to weakly decurved in A. continentale ), longer, wider lateral sepals with a shortly obtuse apex (shorter, narrower and with a drawn-out subacute apex in A. continentale ), and slightly wider, orange labellum (yellow to pale yellow-orange in A. continentale ).

This is the concept of Bulbophyllum tuberculatum following Rupp (1935), not Bulbophyllum tuberculatum ( Colenso 1884: 336) . It is also the concept of Bulbophyllum pygmaeum following Jaede (1962), not Bulbophyllum pygmaeum (Smith in Rees 1819: 411) Lindley (1830: 58). Last, this is the concept of Bulbophyllum exiguum following Mueller (1875), not Bulbophyllum exiguum Mueller (1860: 72) .

Compact herbs with crowded pseudobulbs. Pseudobulbs broadly oblong to elliptical, 3–6 mm long 3–5 mm wide, green, surface smooth, with five or six blunt ribs, shallowly furrowed between ribs, apex flat or shallowly conical. Leaf single; petiole 0.5–2.0 mm; lamina linear to elliptical, 15.0–25.0 × 3.0–6.0 mm, dark green, rigid, midrib sunken, ridged abaxially, margins flat, apex obtuse to apiculate. Racemes arising from base of a pseudobulb, 15.0–30.0 mm long, straight or curved, green to brownish; sterile bract basal on peduncle, narrowly ovate-lanceolate, 4.0 × 2.0 mm, brownish, apex obtuse; peduncle much longer than rachis, 0.5 mm wide, both parts bearing numerous translucent/ whitish silica-like warts. Pedicels 0.5–1.5 mm long, curved, smooth or sparsely verrucose. Ovaries asymmetrically obovoid, 1.0–1.5 × 0.8 mm, green, ribs verrucose. Floral bracts 1.5 mm long, acute. Flowers 1–4, nodding, opening widely, 4.0–4.5 × 4.0–5.0 mm, sepals and petals cream to pale yellow, basal third of labellum pale yellow, distal 2/3 of labellum dark orange. Sepals spreading widely, petals remaining near dorsal sepal, labellum protruding prominently. Dorsal sepal porrect to shallowly incurved, narrowly oblong-cuneate when flattened, 4.0 × 1.3 mm, margins flat, entire, apex subobtuse. Lateral sepals free, widely divergent, 4.5 × 2.3 mm across at widest point near base, broadly asymmetrically ovate-lanceolate when flattened with an expanded basal flange on the anterior margin forming a shallow pouch, midvein thickened, yellowish, exterior surface with irregularly scattered siliceous bumps, apex subobtuse. Petals incurved, partially enclosed by the dorsal sepal, more or less ovate-oblong in outline, 2.5 × 1.0 mm, distal margins irregularly papillate, apex obtuse to subobtuse. Labellum claw attached to labellum base and apex of column foot, ligulate, 0.3 × 0.2 mm. Labellum lamina trilobed, 3.3 mm long when flattened, pale yellow and erect in the proximal 1/3, distal 2/3 recurved more or less at right angles, dark orange; labellum at midpoint of lateral lobes 2.3 mm wide when flattened; lateral lobes erect, curved, 1.5 × 0.8 mm, outer margin broadly rounded; midlobe linguiform, 1.3 × 1.0 mm at base, 0.7 mm thick, basally grooved, convex, thick-textured underside hollow, distal 1/3 recurved, apex obtuse. Callus 2.0 × 1.0 mm, an obscure, oblong, plate-like area between the lateral lobes adorned with two ridges. Column 1.5 × 0.8 mm, white, with incurved wings 0.5 mm wide. Column foot tapered, 0.8 × 0.3 mm, shallowly incurved. Anther ovate, 0.25 ×, 0.20 mm, erostrate. Stigma 0.3 × 0.2 mm, sunken. Pollinarium not seen ( Table 1).

Etymology:—In reference to Lord Howe Island.

Flowering:—April–June.

Distribution:— Lord Howe Island.

Habitat:—In closed rainforest and Drypetes ( Vahl 1807: 49) -Cryptocarya ( Brown 1810: 402) forest, lithophytic on basalt and epiphytic on hosts including Guioa coriacea ( Radlkofer 1878: 326) Radlkofer (1886: 60) (island cedar) and Sarcomelicope simplicifolia (Endl.) Hartley (1982: 369) (bauerella, yellow wood).

Conservation status:—Endemic to Lord Howe Island, which has a total land area of 14.55 km 2. Extent of occurrence and area of occupancy are estimated to be 8 km 2, meeting the geographic range thresholds (<100 km 2 and <10 km 2 for IUCN Red List Criteria B1 and B2, respectively) for critically endangered. It may be at risk from climate change, which is predicted to affect these epiphytic orchids both directly and indirectly through impacts on their habitat in the southern mountains ( Auld & Hutton 2004, Auld & Leishman 2015).

Additional specimens examined:— AUSTRALIA . New South Wales: 10 Nov. 1915, Thompson s.n. (NSW575587); 6 Sep 1963, Beauglehole 5765 (CANB143397); 21 Oct. 1978, Crisp 481 (CBG 7809790); 25 Nov 1985, Hutton 59 (CBG 8317670); 25 Nov 2000, Hutton 782 (NSW492009); Errington 699 (NSW799778).

Figures

FIGURE 5. Adelopetalum howense. A, B. Flower. C, D. Habit. Photos by I. Hutton (A, B), D. Titmuss (C) and G. Walsh (D).