Hydnophytum acuminicalyx Jebb & C.R.Huxley, 2019

28. Hydnophytum acuminicalyx Jebb & C.R.Huxley View in CoL , sp. nov. — Fig. 31 View Fig ; Map 5 View Map 5

Tuber amplectens , complanatum, circulare usque oblongum ambitu, iocineriforme,lobis distinctis,saepe profunde divisis,rotundatis circum marginem ornatum, rotundatis circum marginem ornatum, ad 30 cm in diametro. Aperturae supra omnino nullae, solum in pagina substrata tuberis, ad 2 cm in diametro.Caules numerosi,ramosi,ex stirpe communi enati,in centro tuberis. Folia subsessilia. Lamina obovata ,2 per 1.1 cm sed varia magnitudine,apice acuto, basi cuneata usque sensim attenuata. Inflorescentia binata, sessilis usque breviter pedunculata, instructa bracteis minutis,papyraceis, sed plurimis reliquiis calycum fasciculum distinctum ad nodum quemque formantibus. Calyx 2 mm, irregulariter 4-acumino-dentatus. Flores heterostyli. Corollae tubus 4.5 mm, annulo brevium pilorum ad faucem instructus, lobi 2–3 mm. Pyrenae oblongo-ovoideae, 3.4 per 1.8 mm.

— Typus: Jebb 327 (holo LAE ; iso A, BRI, CANB, K, L, UPNG), Papua New Guinea, Lufa subdistrict , Frigano Timber Lease , Habu River , S6°28' E145°26', 11 May 1983 GoogleMaps .

Etymology. For the prominent and persistent calyx remains with their 4 sharp teeth.

Tuber clasping, flattened, circular to oblong in outline, livershaped, with distinct, often deeply divided, rounded lobes around edge, to 8 by 30 cm; silvery to grey-brown, reddish brown underneath, matt, roughened by minute grooves, sometimes becoming lichen-encrusted, barely corrugated towards edge of lobes and at common stem stock, otherwise smooth and gently undulating. Entrance holes to 2 cm diam, confined to substrate side of tuber only. Cavities numerous, not interconnected, planar to digitate, clasping, warted in their extremities. Flesh white. Roots largely confined to edge of substrate surface. Stems numerous, branching; arising from a common stock at centre of the tuber; to 60 cm long, 0.3–1 cm diam; upcurving, silvery-brown, often lichen-encrusted. Longer shoots with numerous short branches. Internodes on main shoots 0.5–5 cm in length, on secondary shoots 0.1–0.6 cm. Leaves subsessile, clustered at apex, held erect, curving outwards. Lamina obovate, 0.3 by 0.2 to 3.5 by 1.7 cm (most often c. 2.0 by 1.1 cm); apex acute; base cuneate to tapering; fleshy, dark green above, paler below, midrib white, nerves obscure c. 4–6. Petiole 0–0.2 cm, white, rounded; stipules membraneous, blunt, 0.1 cm. Inflorescence paired, sessile to shortly pedunculate, bracts minute papery, often bearing numerous calyx remains (fruit apparently not always produced) forming a distinctive cluster at each node. Flowers [7] heterostylous, lobes apiculate in budCalyx 2 mm, irregularly 4 acumino-dentate, 2 longer than others (1 and 0.4 mm, respectively). Corolla white to yellow-green; tube 4.5 mm, lobes 2–3 mm, a ring of short hairs at mouth of tube. Short-styled flowers with anthers c. 1 mm long, exserted on 1 mm filaments; pollen 60–75 μm, pores 12–14 μm, brochi <1 μm; stigma 2-lobed, at or below level of mouth. Long-styled flowers with anthers 0.6 mm, below level of mouth; pollen 40–50 μm; stigma with 2 papillose lobes c. 1.5 mm long, exserted. Fruit ovoid, to 6 mm overall, crowned by persistent calyx; red, calyx green. Pyrenes oblong-ovoid, 3.4 by 1.8 mm.

Ecology & Habitat — Mid-level epiphyte in closed forest, 2 000–2 400 m; often in large numbers in a single tree. Invariably inhabited by a large form of the aggregate ant species Anonychomyrma scrutator .

Distribution — Papua New Guinea (Eastern Highlands Province).

Conservation status — Critically Endangered (CR) under criteria B1ab(iii)+2ab(iii). The collections indicate just a single location. Other information: AOO 8 km 2 (based on a cell width of 2 km).

Additional specimens examined. Streimann & Kairo NGF 45256 (A, BRI, CANB, K, L, LAE ), Eastern Highlands Province: S6°25' E145°22' Lufa subdistrict, Frigano Timber Lease; Jebb 316 ( LAE ), Jebb 317 ( LAE ), Jebb 318 (BO, CANB, LAE, UPNG ), Jebb 319 (BULOLO), Jebb 320 ( LAE ), Jebb 321 (FHO), Jebb 322 (BRI, K, LAE ), Jebb 323 ( LAE ), Jebb 324 (L, LAE ), Jebb 325 (BISH), Jebb 326 (SUVA), S6°27' E145°26' Lufa subdistrict, Frigano Timber Lease.

Note — The laterally growing tuber of this species, with its smooth, pale to dark-brown, unbroken upper surface, and the prominent and persistent 4-dentate calyces clustered in the axils are unique.