Hydnophytum radicans Becc.

Jebb, M. H. P. & Huxley, C. R., 2019, The tuberous epiphytes of the Rubiaceae 7: a revision of the genus Hydnophytum, Blumea 64, pp. 23-91 : 78-79

50. Hydnophytum radicans Becc. — Fig. 53

Hydnophytum radicans Becc. (1884) 123; (1885) 132, t. 30; Valeton (1911) 503; (1912b) 774; H.J.Lam (1928) 204; Merr. & L.M.Perry (1945) 24. — Type: Beccari 793 (FI), New Guinea, West Papua Province, Andai.

Hydnophytum simplex Becc. (1884) 123; (1885) 129, t. 28. — Type: Beccari s.n. (FI), Indonesia, Maluku Province,Aru Is., Vokan, syn. nov.

Hydnophytum normale Becc. (1884) 123; (1885) 130, t. 29. — Type: Beccari s.n. (FI), New Guinea, Papua Province, Japen Island, Ansus, syn. nov.

Hydnophytum keiense Becc. (1884) 123 (as H. kejense ); (1885) 131, t. 31. — Type: Beccari s.n. (lectotype selected here FI; iso K), Indonesia, Maluku Province, Kei Island, Weri, Aug. 1873, syn. nov.

Hydnophytum subnormale K.Schum. in K.Schum. & Lauterb. (1905) 400; Valeton (1927) 142;Merr.& L.M.Perry (1945) 24. — Type: Nyman 725 (not seen), New Guinea, syn. nov.

Hydnophytum albense Valeton (1927) 128; Merr. & L.M.Perry (1945) 24. — Type: Schlechter 16164 (B presumed lost), New Guinea,Madang Province, Albu, syn. nov.

Hydnophytum kelelense Valeton (1927) 134. — Type: Schlechter 16237 (B presumed lost),New Guinea,Madang Province,Kelel,June 1907,syn.nov.

Hydnophytum montis­kani Valeton (1927) 138 (as H. kaniensis in key, p. 128). — Type: Schlechter 17056 (K), New Guinea, Madang Province, Kani Mountains, 26 Dec. 1907, syn. nov.

Hydnophytum amplifolium S.Moore (1927) 270. — Type: Brass 1151 (lectotype selected here A; iso BRI), Papua New Guinea, Gulf Province, Upoia, Vailala River, 15 Mar. 1926, syn. nov.

Tuber variable, globose to fusiform-cylindric; up to 60 cm broad; surface smooth, grey to brown. Entrance holes few, lipped. Tubers either small and then fleshier with small cavity volume, or larger with very thin cavity walls and large spiral cavities. Stems 1 to several, to 150 cm or more, sparsely branched, thickening towards base; internodes 1.5–15 by 0.2–2 cm. Lamina lanceolate to lanceolate-obovate; 12 by 3 to 27 by 10 cm; apex acuminate, acumen c. 1 cm, rarely to 2 cm, rarely apex acute-acuminate; base rounded to cuneate, attenuate to petiole; midrib occasionally prominent; veins 7–12, oblique; papery to leathery; glossy to dull green. Petiole 1–3 cm long, scarcely winged; stipules triangular, to 0.4 cm. Inflorescence variable; a pair of dichotomously branched (sometimes asymmetrically so) peduncles, branching 1–4 times; terminal branches (numbering 2–8), which are fasciculated and bract-covered, bearing flowers; this terminal portion continues to produce flowers ultimately becoming quite long; in some populations entire inflorescence falling after 4 or 5 nodes from apex; entire inflorescence from 1–15 cm overall, and 0.1–0.5 cm thick at base; rarely bearing a single flower in first or later bifurcations. Flowers [20] not heterostylous. Calyx 1–1.5 mm entire. Corolla 4–7.5 mm overall; lobes 1.5–2 mm; with a ring of hairs in throat. Anthers 1–2 mm; at mouth of tube, 1/2 exserted. Stigma 2-fid, at level of anthers. Fruit globose, to 7 by 5 mm. Pyrenes 2–4, obovoid to oblong, to 4(–5) by 2 mm, flattened; apex notched, blunt or rounded; base rounded.

Ecology & Habitat — In open savannah to closed forest, from sea level to 1 200(–1 800) m, then often a low-level epiphyte. With or without ants, but since there is probably more than one species involved in this complex, each may exhibit a somewhat different ecology in their relationship with ants.

Distribution — Indonesia: Maluku Province (Seram, Kei and Aru islands); West Papua and Papua Provinces (including Yapen Island), Papua New Guinea (mainland only, including Karkar and Normanby Island).

Conservation status — Least Concern (LC). Found across the whole island of New Guinea with herbarium collections indicating over 45 locations (subpopulations). Other information: georeferenced collections 72, EOO over 1 million km 2.

Notes — A very widespread and variable species. Although found throughout the New Guinea mainland, and on some of the offshore islands, H. radicans is absent from the Bismarck Archipelago and the Solomon Islands. We have been unable to resolve any pattern to the variation in this species, and present collections have enabled us to distinguish only two other species: H. albertisii [48] and H. linearifolium [49].

Whilst H. albense , H. amplifolium , H. keiense , H. kelelense , H. montis­kani , H. normale , H. simplex and H. subnormale readily fall into a single variable taxon (even though we have seen no authentic specimens for several of these species), other specimens which are somewhat more extreme in appearance may represent distinct taxa.

Some notable variations are the high altitude collections from the Eastern Highlands Province of Papua New Guinea, which have a large, fusiform tuber with spiral cavities and little tuber flesh (Jebb 93 & 94, Brass 31936 & 32048). It is not occupied by ants, but instead by a range of arthropods, and skinks. The leaves are leathery, with prominent midrib and veins. Another unusual specimen, Brass 7172 (from Western Province, PNG) has remarkably long, slender inflorescences.

Figures

Fig. 53 Hydnophytum radicans Becc. a. Shoot; b. inflorescence detail; c. flower; d. fruit; e. pyrene (a, b: Jebb 427; c–e: after Beccari plate 30). — Scale bars: a = 4 cm; b = 2 cm; c–e = 5 mm. — Drawn by Rosemary Wise.