Dichapetalum auranticarpum W.E.Cooper, sp. nov.

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Type: Australia: Queensland. Cook District: Wattle Hills, Cape York Peninsula, 14 October 2022, W.Cooper 2888, R.Jensen & F.Zich (holo: CNS 154153 [2 sheets + spirit]), iso: 6 sheets to be distributed to BRI, CANB, DNA, L, LAE, MO).

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Figure 2. Dichapetalum auranticarpum: A. Hermaphrodite flower showing apical view of sepals, emarginate petals and anthers; B. Hermaphrodite inflorescence and petioles showing abrupt petiole taper onto abaxial midrib; C. Hermaphrodite inflorescence showing bracts, lateral view of flower buds, scars from dehisced pedicels, sepals and emarginate petals (Cooper 2888, Jensen & Zich [CNS]). D. Fruit showing persistent sepals and petals at base, indumentum and cystoliths (Cooper 2888, Jensen & Zich [CNS]). Photos: A, C & D. F. Zich; B. R. Jensen

Monoecious scandent shrub or vine to c. 5 m; stem diameter to c. 50 mm; bark grey with vertical creases and horizontal lenticels; some branches back-arching; twigs lenticellate, tomentose on new growth becoming thinly appressed, denser at nodes; indumentum white or cream-coloured; stipules caducous, subulate, densely pubescent, c. 2.25 mm long; petioles sub-peltate, thickened, 4–8 mm long not including the taper, taper along abaxial midrib extending for 1.5–2.5 mm, truncated at base of primary vein, taper on adaxial midrib truncate or acute, thinly sericeous, becoming glabrous, dark brown. Leaves oblong-elliptic, oblong-obovate or oblong, 70–130 mm long and 22–53 mm wide, coriaceous; new growth sericeous, denser on primary veins and margins abaxially and adaxially, a tuft of hairs persists at apex of abaxial primary vein but eventually glabrous, glabrescent; glands 3–10 near base abaxially and absent or sparsely scattered over the remainder of the blade; glands on adaxial surface few and scattered; discolorous; base symmetrical and sometimes slightly asymmetrical, cuneate or attenuate, rarely narrowly rounded or subcordate; apex narrowly emarginate, rarely acute or narrowly obtuse and mucronate; margin entire; venation camptodromous proximally and brochidodromous distally; primary vein slightly depressed adaxially and raised abaxially; secondary veins 6 or 7 pairs, raised on both sides, angle to primary vein 40–50º; tertiary venation reticulate, densely pitted within each reticulation on abaxial surface. Hermaphrodite inflorescence an axillary or terminal solitary flower or 2–4-flowered cyme; bracts at base of peduncles lanceolate, 1–2.5 mm long, tomentose; peduncles 1.25–2 mm long, densely pubescent; pedicels articulate, 0.5–1 mm long, densely pubescent; bracts at base caducous, subulate, c. 2 mm long, pubescent; flower fragrance not detected, diameter 3.2–4.5 mm and c. 3.5 mm long; calyx hemispherical at base; sepals ovate, 2.75–4.2 mm long, abaxially and adaxially tomentose; yellowish-green; petals spathulate, folded longitudinally, bilobed and cucullate, apex emarginate to 0.5 mm, 2.75–4.5 mm long, c. 1 mm wide, abaxially with sparse appressed white hairs in lower half, adaxially with sparse hairs along central fold line and margin or almost glabrous, white; stamens 5, glabrous, filaments narrowly triangular and flattened, 1.5–2 mm long, anthers introrse; staminodes bilobed-globose, c. 0.3 mm long, glabrous; ovary globular, 2- or 3-locular, 1.2 x 1.2 mm, tomentose; stigma sessile, c. 0.5 mm long, diameter c. 0.5 mm, 3-lobed, lobes triangular, glabrous. Staminate inflorescence axillary or terminal, 5–24-flowered, glomeruliferous; bracts at base of peduncles and calyces c. 0.5 mm long; peduncles c. 1.75 mm long, tomentose; pedicels absent or up to 1 mm long; Flower fragrance not detected, diameter c. 2.5 mm, c. 2.5 mm long; sepals ovate, 3.2–3.5 mm long, tomentose, yellowish-green; petals 5, free, spathulate, folded, emarginate and cucullate, 3.5–4 mm long, glabrous or a few sparse minute hairs abaxially and adaxially, white; stamens 2.8–3.2 mm long; filaments strap-shaped, c. 2 mm long, glabrous; anthers introrse; staminodes oblate, c. 0.2 mm long, glabrous; pistillode ovoid, diameter 0.5–1.2 mm, tomentose. Fruit peduncle c. 1.3 mm long; thinly sericeous; pedicel absent or minute; drupe 2- or 3-lobed, indehiscent, oblate, diameter 19.5–26.5 mm and 19–22 mm long, immature fruit clothed in arachnoid stellate hairs, mature fruit becoming hairless with cystoliths persisting where the stellate hairs were previously attached, bright reddish-orange, sutures absent; seeds 1–3, sculptured with a distinct rib along the centre abaxially, c. 18.5 x 13 x 9 mm. Figs. 1 & 2.

Specimens examined. Queensland. Cook District: Chester River scrub, eastern fall of McIlwraith Range, Silver Plains Station, June 1992, Forster PIF10443 & Tucker (BRI); Cassowary Creek, Iron Range National Park, April 1993, Fell DGF144A & Butcher (BRI); Wattle Hills, Cape York Peninsula, Oct 2021, Cooper 2798 & Hawkes (CNS); Wattle Hills, Cape York Peninsula, November 2021, Cooper 2821, Addicott & Zich (CNS); Wattle Hills, Cape York Peninsula, November 2021, Cooper 2820, Addicott & Zich (CNS); Wattle Hills, Cape York Peninsula, 15 November 2021, Cooper 2819, Addicott & Zich (CNS); Wattle Hills, Cape York Peninsula, 14 October 2022, Cooper 2887, Jensen & Zich (CNS) ); Wattle Hills, Cape York Peninsula, August 2023, Cooper 3050A & Zich (CNS).

Diagnostic features. Dichapetalum auranticarpum is similar to D. sessiliflorum Leenh. (from New Guinea to Malaysia) but differs from the latter species by the indumentum white or cream (v. rusty); stipules 2.25 mm long (v. 3 mm long); leaf margin entire (v. minutely crenulate); leaf secondary veins 6 or 7 pairs (v. 7–10 pairs); inflorescence pedunculate (v. sessile); hermaphrodite flower diameter 3.2–3.7 mm (v. 2 mm); petals with sparse minute hairs (v. long-pilose); staminodes present (v. absent); fruit epicarp clothed in whitish arachnoid stellate hairs becoming glabrescent (v. densely ferruginous-tomentose); habitat of lowland rainforest below 50 m (v. montane rainforest 1200–1500 m in New Guinea and Malaysia).

Phenology. Flowers have been recorded in April, June, August, October and November and ripe fruit in October and November.

Distribution & habitat. Dichapetalum auranticarpum occurs in mesophyll evergreen rainforest from the Chester River to Wattle Hills on the Pascoe River, including Kutini-Payamu (Iron Range) National Park. The known distribution is in areas of up to 150 m altitude which are inundated by flood waters during the wet season. D. auranticarpum co-occurs with Aglaia euryanthera Harms, Aleurites moluccanus (L.) Wild., Archontophoenix tuckeri Dowe, Argyrodendron polyandrum L.S.Sm., Buchanania arborescens (Blume) Blume, Calophyllum australianum F.Muell. ex Vesque, Castanospermum australe A.Cunn. & Fraser ex Hook., Corymbia tesselaris Benth., Cryptocarya hypospodia F.Muell., Decaisnina hollrungii (K.Schum.) Barlow, Dissiliaria laxinervis Airy Shaw, Donella lanceolata (Blume) Aubrév., Endiandra longipedicellata C.T.White & W.D.Francis, Garcinia dulcis Kurz, Ficus albipila (Miq.) King, Myristica insipida R.Br., Planchonella chartacea (F.Muell. ex Benth.) H.J.Lam, Pongamia pinnata var. minor (Benth.) Domin, Premna hylandiana Munir, Ptychosperma macarthurii (H.Wendl. ex Veitch) H.Wendl. ex Hook.f., Rinorea bengalensis (Wall.) Kuntze, Syzygium bamagense B.Hyland, Syzygium mackinonnianum (B.Hyland) Craven & Biffin and Tetrameles nudiflora R.Br.

Conservation status. Based on known localities, the Extent of Occurrence (EOO) of Dichapetalum auranticarpium is estimated to be 546 km|^2^| with an Area of Occupancy (AOO) of 12 km|^2^| (calculated with GeoCat; Bachman et al. 2011). Sufficient information is not available to make good estimates of population size. The species is known from three locations and is represented in conservation reserves (Kutini-Payamu (Iron Range) National Park).

Based on its EOO and AOO and a severely fragmented distribution or small number (estimated between 5 and 10) of localities (with the threat of severe wildfire as the most serious plausible threat) it meets the thresholds for Criteria B1a + B2a (IUCN 2012).

Recent ‘megafires’ on the Australian continent have demonstrated the risk to mesic ecosystems posed by the combination of changing climate and fire regimes (Jones & Ricketts 2023). Increasing ‘drying’ has seen habitats previously considered not likely to be threatened by fire become susceptible to larger, more intense fires in certain seasons. Given this global phenomenon, it is plausible that an inferred or projected decline in habitat area, extent or quality could be reasonably expected into the future (Sub-criterion b(iii)). Given the most likely preferred habitat for this species is rainforest, it would also not be unreasonable to expect a corresponding projected decline in the number of mature individuals at known locations (Sub-criterion b(v)). Consequently, D. auranticarpum preliminarily satisfies the requirements for listing as VU B1a,b(iii) + B2(a,b(iii) under the IUCN criteria (IUCN 2012) at the National/regional scales.

Etymology. The epithet auranticarpum is derived from the Latin aurantiacus (orange) and carpus ( a fruit), in reference to the bright orange fruit.

Notes. Dichapetalum auranticarpum is notable for its glomeruliferous staminate inflorescences and unusual stellate indumentum on the fruit epicarp.