Hydriastele simbiakii Heatubun, Petoe & W.J. Baker (2018: 18)

Petoe, Peter, Heatubun, Charlie D. & Baker, William J., 2018, A monograph of Hydriastele (Areceae, Arecaceae) in New Guinea and Australia, Phytotaxa 370 (1), pp. 448-450 : 448-450

7. Hydriastele simbiakii Heatubun, Petoe & W.J. Baker (2018: 18) . Type:— INDONESIA. West Papua Province: Tambrauw Regency, Fef Distr. , Sungai Sujak (Sungai Eyei), river bank near bridge, 400 m, 0°50’S, 132°30’E, 23 January 2013, Baker et al. 1365 (holotype K!, isotypes AAU!, BO!, L!, MAN!)

Figure 15 (line drawing). Figure 16 (photo plate). Figure 14 (map).

Clustering, very slender rheophytic palm forming clumps of often numerous stems, to 5–6 m tall, bearing ca. 6–7 leaves per crown. Stem 1.5–2.5 cm in diam., pliable, shorter stems erect, longer stems leaning over river. Leaf 64–104 cm long including petiole; sheath 26–36 cm long; petiole 12–25 cm long; leaflets 14–16 per side, regularly arranged, single- or multi-fold, linear, praemorse apically. Inflorescence 13–17 cm long including 1.5–3 cm peduncle, branched to 1 order, protandrous; rachillae 3–4, scarlet; triads spirally arranged. Staminate flower 10–11 × 5–6 mm at anthesis, pink; stamens 6. Pistillate flower 4–5.5 × 2–3 mm post-anthesis, white with pinkish tinge, with free sepals and free petals with conspicuous, triangular tips. Fruit 8–12 × 4–5 mm when ripe, ellipsoid, red, with a distinct, dark, sclerotic zone encircling apical stigmatic remains (up to ca. 2 mm in diam.). Seed 7–8 × 4 mm, ellipsoid; endosperm ruminate.

Distribution:— Known only from the type locality in the Tamrau Mountains of the Bird’s Head Peninsula in western New Guinea.

Habitat:— Steep, rocky river margin in the flood zone ca. 1–2 m above fast flowing water, 400 m.

Uses:— Stems used for making spears.

Vernacular names:— None recorded.

Conservation status:— Data deficient (DD; Heatubun et al. 2018).

Specimens examined:— INDONESIA. West Papua Province: Tambrauw Regency, Fef Distr., Sungai Sujak (Sungai Eyei), river bank near bridge, 400 m, 0°50’S, 132°30’E, 23 January 2013, Baker et al. 1365 (AAU!, BO!, K!, L!, MAN!) .

Notes:— Hydriastele simbiakii is one of two strictly rheophytic species known from the genus Hydriastele , the other being H. rheophytica from the Wendlandiana group. Hydriastele simbiakii forms distinctive clumps of pliable stems, the taller ones becoming leaning and is further distinguished by displaying 14–16 regularly arranged, linear leaflets on each side of the rachis, and ruminate endosperm. Hydriastele simbiakii is most easily confused with rare forms of H. pinangoides displaying regularly pinnate leaves and similar inflorescences, but H. simbiakii is distinguished from these forms by its ecological preference and leaves with more numerous leaflets. Hydriastele simbiakii is described in more detail by Heatubun et al. (2018).

Figures

FIGURE 14. Distribution map of part of the species of the Nengella group of Hydriastele.

FIGURE 15. Hydriastele simbiakii. A. Habit. B. Leaf diagram. C. Leaf apex. D. Leaf base. E. Inflorescence with pistillate flowers. F. Portion of rachilla with pistillate flowers. G. Staminate flower whole and in longitudinal section. H. Pistillate flower whole and in longitudinal section. I. Portion of rachilla with fruit. J. Fruit in longitudinal section. Scale bar A = 60 cm; B = 24 cm; C–D = 6 cm; E = 4 cm; F–G, I = 8 mm; H = 4 mm; J = 7 mm. All from Baker et al. 1365. Drawn by Lucy T. Smith.

FIGURE 16. Hydriastele simbiakii. A. Habit. B. Inflorescences with pistillate flowers (left) and complete triads (right). C. Portions of rachillae with pistillate flowers. All from Baker et al. 1365. All photos: W.J. Baker.