Hydnophytum petiolatum var. argentatum, 2019

b. var. argentatum Jebb & C.R.Huxley View in CoL , var. nov. — Map 3

a Hydnophytum petiolatum sed tuber oblongum , angulari,superficies laevis, argentum coloratum. Folia subsessilia, lamina subrotunda usque ovata, 1.1 per 0.8 ad 3.4 per 3 cm,apice obtusa vel rotundato,basi obtusa vel cordata, nervi obscurato 4–5. Petiolus brevissimus. Pyrenae obovoideae, 4 per 2.5 mm, apice rotundato vel acuminato minuto, basi attenuata.

View Map 3

— Typus: Jebb 376 (holo K; iso L, LAE, UPNG), Papua New Guinea, Milne Bay Province, Normanby Island, Mt Bwebwesu, 6 June 1983 .

Etymology. For the silver colour of the tuber surface in the living plant.

Tuber oblong-ovoid, angular, to 25 by 14 cm, silvery-grey in colour. Entrance holes varied in size, 0.2–1.8 cm, all more or less prominently lipped. Stems numerous, regularly branching, rounded in section; nodes swollen, to 7 mm across, internodes 0.4–4.5 cm. Leaves clustered at stem apices. Lamina roundelliptic; 1.1 by 0.8 to 3.4 by 3.0 cm; apex blunt to rounded; base blunt to cordate; veins 4 or 5; drying dark above pale below. Petiole very short; stipules triangular, 0.1 cm, persistent becoming worn. Inflorescence sunken, 0.4–0.5 cm across, and densely filled with papery bract remains and bract hairs to 0.3 cm long. Flowers [5] heterostylous. Calyx 1.5 mm, entire, with a large number of brown bract hairs arising from its surface, and persistent in fruit. Corolla tube to 4.5 mm, lobes 2 mm, with a ring of hairs at mouth of tube. Short-styled flower with anthers exserted, to 1.5 mm, pollen 38–45 µm diam; stigma at or slightly below anthers. Long-styled flower with anthers within tube, to 1 mm, pollen 35–37 µm diam; stigma exserted. Fruit 4.5 by 3 mm, red. Pyrenes obovoid, 4 by 2.5 mm; apex rounded, minutely acuminate; base attenuate.

Ecology & Habitat — Only known from the stunted, scrub forest on ultrabasic soils in southern Normanby Island, from 400–600 m ( H. dentrecastense [43] and Anthorrhiza areolata C.R.Huxley & Jebb (1991b) are also endemic to this area of vegetation). The tuber cavities contain rainwater and cockroaches.

Distribution — Papua New Guinea (Normanby Island).

Conservation status — Vulnerable (VU) under criteria D2 with a single population known from an area of ultramafic soils identified as a source of future nickel and gold mining. The entire area covers less than 20 km 2, but it is not known whether this epiphyte is found further afield.

Additional specimens examined. Jebb 375 ( LAE ), Jebb 377 (A), Jebb 378 ( LAE ), Jebb 379 ( LAE ), Milne Bay Province, Normanby Island: S10°02' E151°00', NW slopes of Mt Bwebwesu, above Sewa Bay, 6 June 1983.

Note — This variant has slender, much contorted stems, and small, almost circular leaves. The tuber has a smooth surface, with prominently lipped entrance holes. It is named for the striking metallic silver-coloured surface of the tuber.