Rhopaloblaste gideonii Banka

Baker, W.J., Barfod, A.S., Cámara-Leret, R., Dowe, J.L., Heatubun, C.D., Petoe, P., Turner, J.H., Zona, S. & Dransfield, J. (2024) Palms of New Guinea. Royal Botanic Gardens, Kew, Richmond. 726 pp.

Morphology General Habit

Moderately robust, single-stemmed palm to 25 m

Morphology Stem

Stem ca. 20 cm diam. Leaf to 4 m long including petiole; sheath 55–65 cm long; petiole 8–10 cm long; leaflets 100–103 each side of rachis, linear-elliptic, lower surface with few ramenta on midrib; mid-leaf leaflet 72–80 × 1.5–2.5 cm

Morphology Reproductive morphology Inflorescences

Inflorescence 58–65 cm long including 1–2 cm peduncle, widely spreading with basal branches strongly recurved, branched to 2 orders; primary branches 12–13, to 60 cm long, rachillae 42–54 cm long, 6–6.5 mm diam. Male flower 7–7.5 × 3.8–4.1 mm at anthesis

Morphology Reproductive morphology Flowers

Female flower 5–5.5 × 5.2–5.4 mm

Morphology Reproductive morphology Fruits

Fruit 16–18 mm × 6–8 mm (only immature fruits seen), ellipsoid-ovoid

Morphology Reproductive morphology Seeds

Seed not seen.

Distribution

Known only from the type locality in the Hans Meyer Range, New Ireland.

Ecology

Lower montane forest at ca. 800 m.

Vernacular

None recorded.

Conservation

Data deficient (IUCN 2021). This species is insufficiently known to allow completion of an assessment. It is known only from one site, but this appears to be in pristine forest, so could be assessed as either Least Concern or Critically Endangered. The assessment reflects this uncertainty.

Note

This poorly known species appears to be similar to Rhopaloblaste ceramica, but is easily distinguished by its inflorescences that are branched to two orders only and by the smaller cupule of persistent perianth on the fruit. The type locality is also substantially disjunct from the known distribution of the other two New Guinea species. It is also distinct from the nearest species to the east (R. elegans from the Solomon Islands) in fruit shape (ellipsoid-ovoid, rather than spherical) and the more robust rachillae.

IUCN Red List of Threatened Species https://www.iucnredlist.org/species/167561167/185833882

Conservation

DD - data deficient

Banka, R., & Baker, W. (2004). A Monograph of the Genus Rhopaloblaste (Arecaceae). Kew Bulletin, 59(1), 47-60. doi:10.2307/4111073

Type

Papua New Guinea, New Ireland Province, Namatanai Distr., Hans Meyer Range, 70 km SE of Namatanai, Nov. 1984, Gideon et al. NGF 57194 (holotypus L!; isotypus LAE!).

Morphology General Habit

Moderately robust solitary palm

Morphology Stem

Stem to 25 m tall, c. 20 cm diam.; leaf scars prominent; surface greyish brown

Morphology Leaves

Leaf sheath 55 - 65 cm long, greyish brown, densely lepidote-tomentose with whitish brown interlocking scales; crownshaft 60 - 70 cm long, 27 - 30 cm wide; petiole short, 8 - 10 cm long, concave on adaxial surface, greyish brown; rachis 3 - 4 m long, with white to greyish brown membranous scales, denser on the adaxial surface; leaflets 100 - 103 each side of rachis, borne 2.5 - 3 cm apart, in one plane, semi-pendulous, middle leaflet 72 - 80 cm long, 1.5 - 2.5 cm wide, elliptic-linear, tapering acutely and bifid at the apex, adaxial surface green, abaxial surface light green with ramenta present sparsely along the mid veins on the abaxial surface, greyish brown to black membranous scales present on adaxial surface of mid-veins especially near the base of pinnae

Morphology Reproductive morphology Inflorescences

Inflorescence 58 - 65 cm long, branched to 2 orders; primary branches 12 - 13, 50 - 60 cm long, basal pair of primary branches strongly recurved; prophyll 29 - 38 x 7 - 8.5 cm, silky-tomentose; peduncle 1 - 2 cm long, 1.5 - 2.3 cm diam.; rachillae moderately robust, 42 - 54 cm long, 6 - 6.5 mm diam. Staminate flower symmetric, 7 - 7.5 mm long, 3.8 - 4.1 mm diam. at anthesis; sepals 2.4 - 2.5 x 2 -2.4 mm, rounded and imbricate; petals 6 - 6.1 x 4 - 4.1 mm, broadly elliptic; stamens 6.6 - 6.8 mm long, filaments 2.5 - 3 mm long, connate at the base, anthers 3.7 - 3.8 mm long, 1 - 1.1 mm diam., elliptic; pistillode conical, 3.5 - 3.6 mm long, 1 - 1.2 mm diam. at the base

Morphology Reproductive morphology Flowers

Pistillate flower 5 - 5.5 mm long, 5.2 - 5.4 mm diam., borne abundantly on the proximal portion of the rachillae, then fewer distally; sepals 4 - 4.1 x 5.8 - 6 mm, rounded and asymmetrical; petals 4.3 - 4.4 x 3.5 - 3.6 mm, broadly elliptic, apex with 1 mm acute tip, sparse brownish hairs on the middle part of the margin; staminodes 4, lobes 1 - 1.1 x 0.2 - 0.3 mm at the base, acute at the apex; gynoecium 3.8 - 4 mm long, 3.3 - 3.5 mm wide, ovoid

Morphology Reproductive morphology Fruits

Fruit only immature fruit seen, 16 - 18 mm long, 6 - 8 mm diam., ellipsoid-ovoid; cupule of persistent perianth 8.5 - 9 mm long.

Distribution

Known only from the type locality in the Hans Meyer Range, New Ireland.

Ecology

Lower montane forest at 800 m above sea level, dominated by Serianthes and Elmerillia species.

Conservation

Data deficient. The forests of New Ireland have been extensively logged. The conservation status of this endemic palm should be evaluated at the earliest opportunity.

Note

This new species is known only from the type locality and cannot be readily equated with other species. It is easily distinguished from two of the Papuasian species, R. ledermanniana and R. elegans, on account of its robust fruit-bearing rachillae. It resembles R. ceramica in its moderately robust fruit- bearing rachillae, but differs in bearing inflorescences branched to two orders only and a smaller cupule of persistent perianth on the fruit. In R. ceramica, the inflorescences are branched to three orders and the fruit bears a large, robust cupule of persistent perianth. While the fruit on the type of R. gideonii are immature, the persistent perianth is significantly less robust than that of immature R. ceramica fruit. In addition, the type locality is disjunct from the known distribution of R. ceramica in Sandaun Province, Papua New Guinea. Rhopaloblaste gideonii is named for the collector of the type specimen, Osia Gideon, formerly Principal Botanist at the LAE Herbarium (Papua New Guinea Forest Research Institute), now lecturer in the Biology Department at the University of Papua New Guinea, in recognition of his contributions to botany in Papua New Guinea.

Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592

Conservation

Predicted extinction risk: threatened. Confidence: confident

Use

None recorded.