Hydriaste biakensis Baker & Heatubun 2012
Creators: name: Petoe, Peter
name: Heatubun, Charlie D.
name: Baker, William J.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Fabales
Fabaceae
Hydriaste
Hydriaste biakensis

description: 24. Hydriaste biakensis Baker & Heatubun (2012: 144–150). Type:— INDONESIA. Papua Province: Biak Island, Oridek distr., Wadibu village, 1°8’32”S, 136°18’11”E, July 2009, Baker et al. 1342 (holotype K!, isotypes AAU!, BO, MAN)   
Figure 52 (line drawing). Figure 53 (photo plate). Figure 54 (map).  
 Solitary, robust palm to ca. 15 m tall bearing 18–24 leaves in crown. Stem ca. 30 cm in diam. Leaf ca. 3.3–3.6 m long including petiole; sheath ca. 170 cm long; petiole ca. 47–50 cm long; rachis strongly arcuate; leaflets ca. 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 ca. 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 ca. 1 mm in diam.). Seed 7.5–8.2 × 4–4.3 mm, cylindrical; endosperm homogeneous.   
 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.   
 Uses:— Stems and leaf sheaths used for flooring and baskets respectively.   
 Vernacular names:— Arwaf (Biak).   
 Conservation status:— Endangered (EN; Baker & Heatubun 2012).   
 Specimens examined:— INDONESIA. Papua Province: Biak Island, Oridek distr., Wadibu village, 1°8’32”S, 136°18’11”E, 24 July 2009, Baker et al. 1342 (AAU!, BO, K!, MAN); Same locality as preceding, 1°8’32”S, 136°18’11”E, 24 July 2009, Heatubun 970 (BO!, K!, MAN!, NY!); Numfoor Island, 01°03’15.6” S 134°49’17.8”E, 11 November 2012, Heatubun 1225 (MAN, K!).   
 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).
description: Published as part of Petoe, Peter, Heatubun, Charlie D. & Baker, William J., 2018, A monograph of Hydriastele (Areceae, Arecaceae) in New Guinea and Australia, pp. 448-450 in Phytotaxa 370 (1) on pages 448-450, DOI: 10.11646/phytotaxa.370.1.1, http://zenodo.org/record/13705467