Hydriastele biakensis

Hydriastele (high-dree-Ah-STEL-eh) biakensis (bee-ah-KEHN-siss)
Marau, Biak, Indonesia. Photo by Dr. William J. Baker, Royal Botanic Gardens, Kew/Palmweb.
Scientific Classification
Genus: Hydriastele (high-dree-Ah-STEL-eh) Species: biakensis (bee-ah-KEHN-siss)
Synonyms
None set.
Native Continent
Oceania
Morphology
Habit: Solitary Leaf type: Pinnate
Culture
Survivability index
Common names
Arwaf (Biak dialect), Biak Nymph Palm.

Habitat and Distribution

New Guinea. Known from few specimen localities and sight records on the south and western

Near Tanjung Warari, Biak, Indonesia. Photo by Dr. William J. Baker, Royal Botanic Gardens, Kew/Palmweb.

coast of Biak and Auki Island on the nearby Padaido Islands. Coastal forest on limestone near to sea level, sometimes on limestone cliffs close to the beach.

Distribution:—Numfoor Island and Biak Island. May also occur on the nearby Auki Island (Baker & Heatubun 2012).

Habitat:—Coastal forest near beach or on cliff edges, on rugged limestone with very thin or no topsoil, near to sea level. PETER PETOE, CHARLIE D. HEATUBUN & WILLIAM J. BAKER Phytotaxa 370 (1) © 2018 Magnolia Press.

Description

Solitary, robust palm to ca. 15 m tall bearing 18–24 leaves in crown. Stem about 30 cm in diam. Leaf about 3.3–3.6 m long including petiole; sheath about 170 cm long; petiole about 47–50 cm long; rachis strongly arcuate; leaflets about 65 per side, arranged regularly, single-fold, ascending and sometimes ± drooping at their tips, linear acuminate or sometimes briefly bifid to obliquely praemorse apically, with ramenta attached to the basal portion of the abaxial side of the midrib; middle leaflet 121–126 × 3–4.5 cm. Inflorescence 95–100 cm long including 19–21 cm peduncle, branched to 4 orders, apparently protogynous, with pronounced “shoulders” formed by the abrupt constriction of the peduncle right above the prophyll scar; prophyll often ± sigmoid, with pithy keels; rachillae sinuous, especially towards the tip; triads 3–7 mm apart, opposite and decussate. Staminate flower 5–6.5 × 2.5–4 mm in bud, white; stamens 6, exposed in bud. Pistillate flower about 2.5 × 2.5–2.8 mm in bud, with free sepals and free, low and ± rounded petals. Fruit 9.5–12 × 5–6 mm when ripe, narrowly ellipsoid, red, with inconspicuous sclerotic zone encircling apical stigmatic remains (up to about 1 mm in diam.). Seed 7.5–8.2 × 4–4.3 mm, cylindrical; endosperm homogeneous. PETER PETOE, CHARLIE D. HEATUBUN & WILLIAM J. BAKER Phytotaxa 370 (1) © 2018 Magnolia Press.

Notes:—Hydriastele biakensis is endemic to the Biak Islands and is the only canopy species of the genus recorded from this area other than H. costata. Unlike H. costata, H. biakensis has a recurved crown, but differs from similar species in that its terminal leaflets are single-fold and pointed or shallowly notched at their tips (not truncately praemorse). In addition, its staminate flowers are congenitally open in bud and its prophyll is often somewhat distorted, features that are shared with the Australian H. ramsayi, but H. biakensis is distinguished from this, and all other species in the genus, by its inflorescence branched to 4 orders with markedly sinuous rachillae and a peduncle with prominent “shoulders” resulting from an abrupt constriction by the prophyll scar. Hydriastele biakensis is strongly supported as sister species to the smaller H. palauensis (Loo et al. 2006, Baker & Heatubun 2012), which is endemic to the Pacific island nation of Palau and, like H. biakensis, has staminate flowers that are congenitally open in bud (see Baker & Heatubun 2012). PETER PETOE, CHARLIE D. HEATUBUN & WILLIAM J. BAKER Phytotaxa 370 (1) © 2018 Magnolia Press.

Robust, solitary, canopy palm. Stem about 15 m tall, about 30 cm in diam., leaf scars prominent, internodes 3-7 cm, surface brown. Leaves about 18-24 in the crown, strongly recurved; sheath about 170 cm long, pale green with white waxy indumentum, striate near mouth, forming crownshaft 200-270 cm long, 26-27 cm wide; rachis 280-300 cm long, petiole 47-50 cm long, 3.5-5 cm wide, channeled adaxially, petiole and lower rachis yellowish green, petiole and rachis bearing scattered to dense brown, caducous, felty indumentum and minute dark dots throughout; leaflets about 65 each side of rachis, regularly arranged, strongly ascending, concolorous, with minute dark dots abaxially, brown, basifixed ramenta attached to basal, abaxial portion of midrib; middle leaflets 121-126 cm long, 3-4.5 cm wide, linear, transverse veinlets conspicuous, apices narrowly acute; terminal segments linear, with apices notched, not praemorse. Inflorescence 95?100 cm long, infrafoliar, ?protandrous, horsetail-shaped, erect, branched to 4 orders, axes white on emergence, turning green; prophyll 70-107 cm long, 15-18 cm wide, green, often somewhat sinuous, appearing distorted, keels pithy, with thin, white with thin, white indumentum; first peduncular bract, about 70 cm long, about 5.5 cm wide, similar to prophyll, attached 2.5-4.5 cm above prophyll insertion; peduncle 10-21 cm long, 8-8.5 cm wide at base, narrowing sharply above prophyll insertion to 3-3.5 cm, prophyll scar conspicuous with rounded "shoulders"; primary branches 20-22, the longest (basalmost) to 70 cm; rachillae 32-48 mm long, 2-3 mm in diam., sinuous, especially distally, triads 2-3 mm apart, decussate. Staminate flower 5-6.5 mm long, 2.5-4 mm in diam. in bud, variously flattened and distorted, congenitally open; sepals connate in a shallow cup with three triangular lobes ca. 0.5 mm long, white; petals 5-6 mm long, 1-1.5 mm wide, narrowly triangular, variously twisted and sinuous, briefly adnate to receptacle, white; stamens 6, 4.5-5.5 mm long, white; filaments ca. 0.5 mm long, narrowly conoid; anthers 4-5 mm long, 0.8-1.2 mm wide, oblong to sinuous, basifixed, dehiscence latrorse; pistillode minute, pyriform. Pistillate flower about 2.5 mm long, 2.5-2.8 mm in diam., borne throughout the rachillae; sepals imbricate, about 1 mm long, 2.5-2.8 mm wide, rounded, white; petals 2-2.5 mm long, 2.5-3 mm wide, strongly imbricate, rounded, white; staminodes 3, minute, paddle-shaped; gynoecium about 2 mm long, about 1.5 mm in diam., globose; stigma minutely trifid. Fruit 9.5-12 mm long, 5-6 mm in diam., oblongellipsoid, red, perianth cupule clasping, endocarp thin, tough, closely adhering to seed. Seed 7.5-8.2 mm long, 4-4.3 mm in diam., cylindrical; endosperm homogeneous; embryo basal. (W.J.Baker & C.D.Heatubun, New Palms from Biak and Supiori, Western New Guinea in Palms (1999+) 56(3). 2012)/Palmweb. Editing by edric.

Culture

Cold Hardiness Zone: 10b