Adelopetalum argyropus (Endl.) D.L.Jones & M.A.Clem.

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 : 86-88

Adelopetalum argyropus (Endl.) D.L.Jones & M.A.Clem. ( Figs 1–3 )

Basionym: Thelychiton argyropus Endl.

TYPE: — AUSTRALIA . Norfolk Island: Bauer s.n. (lectotype, inadvertently designated by Clements (1989): W0046213!; isolectotype: K).

Homotypic synonym: Bulbophyllum argyropus (Endl.) Reichenbach (1876: 42) (1876).

Small to large, compact herbs with crowded sympodia. Roots thin, white, elongate, unbranched. Emerging shoots covered with white, felted, fugacious bracts. Pseudobulbs broadly oblong to obconical or turbinate (similar to a cupcake, “ poculum crustulam simile ”), 5.0–10.0 × 4.0–6.0 mm, margins with 4–5 weakly angular ribs, surface shallowly grooved, scurfy from remnants of fugacious bracts, apex truncate with shallow to deep depressions. Leaf single, petiole 1–2 mm long; lamina narrowly to broadly elliptic, 10.0–30.0 × 3.0–6.0 mm, dark green, rigid, shallowly grooved adaxially along the midrib, underside with a weak central keel, apex obtusely apiculate. Racemes arising from base of a pseudobulb, 20.0–30.0 mm long, shallowly curved; sterile bract basal on peduncle, narrowly ovate-lanceolate, 6.0 × 2.5 mm, green ageing brown, apex acuminate; peduncle much longer than rachis, 0.7 mm wide, pale green, bearing numerous minute translucent/whitish silica-like warts. Floral bracts ovate-lanceolate, pale green, basally sheathing the pedicel, 1.5 × 1.0 mm. Pedicels 1.0 mm long, green, smooth, incurved at apex. Ovaries obovoid, straight, 1.5 × 1.0 mm, green, with numerous minute translucent/whitish crystal-like warts. Flowers 1–4, not opening widely, porrect to weakly decurved, 4.0 × 2.5 mm, cream to greenish white. Sepals and petals not opening widely, labellum not longer than sepals. Dorsal sepal porrect, oblong-elliptic, 4.0 × 1.2 mm, external surface weakly and irregularly verrucose, apex acute to mucronate. Lateral sepals free, weakly divergent, ovate-oblong, 4.0 × 1.4 mm, external surface weakly and irregularly verrucose, apex subacute to mucronate. Petals porrect to weakly divergent, mostly overlapped by the sepals, oblong-elliptic, 3.0 × 1.0 mm, apex subobtuse to subacute. Labellum lamina entire, petaloid, cream to greenish white, narrowly elliptic, 3.0 mm long. Column 1.0 mm wide with prominent stigmatic cavity, partially covered from base by central lobe. Anther cap cordate, possibly colluviate. Capsules broadly elliptical, 6.0 × 5.0 mm, ribs with minute translucent/whitish silica-like warts. ( Fig. 1 )

Etymology:—From argyros (silver), - pous, podos (foot), referring to silvery scales on young pseudobulbs (probably scurfy remnants of fugacious bracts).

Flowering: — May (authors’ observations), August–September ( Green 1994).

Distribution: — Norfolk Island.

Habitat:—Epiphytic in upland hardwood and pine hardwood ridge forests, in areas with above-average air circulation (based on authors’ observations; Zimmer 2023). Host species include Didymocheton bijugus ( Labillardière 1825: 54) Holzmeyer & Mabberley in Holzmeyer et al. (2021: 1259) (sharkwood).

Conservation status:—Endemic to two sites with total land area of 34.6 km 2. Extent of occurrence and area of occupancy are estimated to be 12 km 2, meeting the geographic range threshold (<100 km 2 for IUCN Red List criterion B1) for assessment as critically endangered. It is at risk of continuing decline due its restricted habitat (moist upland hardwood forest on Norfolk Island) and the impacts of climate change, in particular drought. Mean annual rainfall on Norfolk Island has declined 11% between 1970 and 2020 ( CSIRO 2020).

Additional specimens examined:— 17 Oct. 1993, Christian & Cochrane ESW48 (CBG 9602070); 18 May 2022, Clements 13711 (CANB 999452); 30 Nov 1996, Zeising 350 (CANB 616544); Bauer s.n. (W0046213). [https://plants. jstor.org/stable/10.5555/al.ap.specimen.w0046213]; Bauer s.n. (K000867047) [https://plants.jstor.org/stable/10.5555/ al.ap.specimen.k000867047].

Figures

FIGURE 1. Adelopetalum argyropus (as Thelychiton argyropus) illustrated in plate 29 of part 3 of Endlicher’s Iconographia generum plantarum (1837). BHL affirms that this work is in the public domain. Source: https://www.biodiversitylibrary.org/page/41749924.

FIGURE 2. Adelopetalum argyropus, collected by Ferdinand Bauer from Norfolk Island (as Thelychiton argyropus). Royal Botanic Gardens, Kew, K000867047. Available online from http://specimens.kew.org/herbarium/ K000867047. © RBG Kew.

FIGURE 3. Adelopetalum argyropus. A, C. Flower. B. Habit. Photos taken in situ on Norfolk Island. Photos by H. Zimmer and M. Clements.