Hydriastele H.Wendl. & Drude, Linnaea 39: 208 (1875)

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Discussion

  • Uhl and Dransfield (1987) indicated that generic delimitation among the Papuasian members of Arecinae was problematic. In the first edition of Genera Palmarum, four Papuasian genera were assigned to Arecinae, together with Areca, Nenga, Pinanga and Loxococcus. Uhl and Dransfield placed emphasis on aspects of floral morphology that seemed to be correlated with protandry and protogyny. Species in which the pistillate flowers have large triangular petals closely adpressed in bud (Gronophyllum and Siphokentia) seemed to be protandrous, whereas those with inconspicuous rounded petals with minute triangular tips (Hydriastele and Gulubia) seemed to be protogynous. This apparently neat correlation was, however, based on very few observations of the sequence of flowering and was in the most part inferred. Furthermore, this delimitation resulted in genera of sometimes disparate habit. Recent phylogenetic studies (Loo et al. 2006) strongly support the monophyly of the Papuasian clade. Within the clade, however, only Hydriastele is monophyletic; Gronophyllum and Gulubia are polyphyletic with members of both genera resolving in a number of separate, highly supported groups with members of other genera within the clade. The position of Siphokentia is ambiguous but this genus, along with Hydriastele, is deeply nested within the clade. It has not been possible to find morphological characters that differentiate most of the groupings resolved in the molecular studies, and thus it is not possible to alter the generic delimitation to reflect the molecular phylogeny. For these reasons, we have followed Baker and Loo’s proposal (2004) to accept a single genus, for which the earliest name is Hydriastele. (J. Dransfield & N. Uhl & C. Asmussen & W.J. Baker & M. Harley & C. Lewis, Genera Palmarum. The evolution and classification of palms. 2008)

Diagnosis

Biology And Ecology

Etymology

Uses

Description

  • Small, moderate or tall, solitary or clustered, unarmed, pleonanthic, monoecious palms. Stems erect, slender to robust, bare, conspicuously ringed with leaf scars. Leaves entire-bifid or pinnate, neatly abscising; sheaths elongate, forming a well-defined crownshaft, usually densely scaly or tomentose, and/or waxy, a ligule-like prolongation sometimes present opposite or at the base of the petiole; petiole short to long, adaxially channelled, abaxially rounded, usually conspicuously scaly; rachis adaxially channelled or angled near the base, distally angled, abaxially rounded, usually scaly as the petiole; leaflets regularly arranged, or grouped, pendulous or horizontal or ascending, straight or curved, single-fold or several-fold, the terminal pair usually broad, several-fold, the rest parallel sided or somewhat wedge-shaped, apically acute, bifid or conspicuously praemorse, adaxial and abaxial surfaces bearing scattered minute scales, abaxially sometimes with scattered ramenta along the main veins, sometimes also with bands of deciduous chaffy scales along major ribs, transverse veinlets conspicuous or obscure. Inflorescences infrafoliar, branching to 1–3 orders or rarely spicate, usually horsetail-like, protandrous or protogynous; peduncle short, winged at the base, sometimes becoming swollen; prophyll compressed, entirely enclosing the inflorescence in bud, 2-keeled, with a conspicuous apical beak, thin, papery when dry, glabrous or scaly, soon drying on exposure, splitting longitudinally on the abaxial face and abscising together with the peduncular bract; peduncular bract 1 rarely 2, similar to and entirely enclosed by the prophyll, tubular, enclosing the inflorescence in bud; subsequent bracts inconspicuous; rachis (where present) longer or shorter than the peduncle, bearing inconspicuous rachis bracts subtending few to many crowded, ± spirally arranged first-order branches, the proximal bearing a few branches or all unbranched; rachillae elongate, usually ± straight or curved, of ± equal length, tending to curve downwards, bearing throughout their length spirally arranged or opposite and decussate pairs of triads of cream-coloured or pinkish-tinged flowers, except at the very tip where bearing solitary or paired staminate flowers; rachilla bracts very inconspicuous, low, ± rounded. Staminate flowers fleshy, asymmetrical; calyx sessile or with a short stalk-like base, sepals 3, short, triangular, ± distinct or joined into a cup for ca. 1/2 their length; petals 3, fleshy, distinct, except at the very base, valvate except in Hydriastele palauensis where margins not meeting triangular, asymmetric; aperture a distal sulcus or trichotomosulcus; in bud, 4–5 times as long as the calyx, narrow, triangular, 1 usually larger ectexine tectate, coarsely perforate, foveolate, coarsely perforate-than the other 2; stamens 6–24, epipetalous, filaments very short, fleshy, rugulate or rarely scabrate verrucate, aperture margin similar; longest variously epipetalous and connate, anthers elongate, erect, basifixed, axis ranging from 33–70 µm; post-meiotic tetrads tetragonal or latrorse, connective sometimes prolonged into a short point; pistillode tetrahedral [22/47]. Pistillate flowers globose or ± conical in bud, smaller absent. Pollen ellipsoidal, bi-symmetric; aperture a distal sulcus, brevi-, ± than the staminate; sepals 3, distinct, rounded or triangular, broadly same length as long axis or, frequently, extended; ectexine semi-tectate imbricate or connate in a ring with 3 low triangular lobes; petals 3, and coarsely (rarely finely) reticulate, muri of reticulum sometimes distinct or connate, not more than to at least twice as long as the sepals, perforate, aperture margins similar; or pollen ellipsoidal or oblate-rounded or triangular, basally broadly imbricate or connate in a ring, apically rounded except for very small triangular valvate tips or with conspicuous triangular valvate tips, closely appressed in bud, the tips persisting or eroding into fibres in fruit; staminodes 3(–6), tooth-like, minute; gynoecium ± globose or ovoid, unilocular, uniovulate, stigmas 3, low, sessile or fleshy, reflexed, ovule laterally attached near apex of locule, hemianatropus (?always). Fruit globose to narrowly ellipsoidal, straight or curved, bright red to purplish-black, sometimes drying ridged, sometimes briefly beaked, stigmatic remains apical, perianth whorls persistent, the petal tips sometimes reflexed or appressed to the fruit; epicarp smooth or slightly pebbled, mesocarp thin, with abundant tannin cells, and longitudinal fibre bundles, endocarp thin, crustose or obsolescent. Seed ovoid or globose, laterally or basally attached with elongate or rounded hilum, raphe branches sparse, anastomosing, endosperm homogeneous or shallowly to deeply ruminate; embryo basal. Germination adjacent-ligular; eophyll bifid with entire or minutely to strongly praemorse tips. Cytology: 2n = 32. (J. Dransfield & N. Uhl & C. Asmussen & W.J. Baker & M. Harley & C. Lewis, Genera Palmarum. The evolution and classification of palms. 2008)

Fossil record

Relationships

  • Hydriastele is moderately to highly supported as a monophyletic genus following the recent inclusion of three genera, Gronophyllum, Gulubia and Siphokentia, in synonymy (Baker and Loo 2004, Asmussen et al. 2006, Loo et al. 2006, Norup et al. 2006, Baker et al. in prep.). The relationships of Hydriastele remain unclear, but it is worth noting that, in the most densely sampled studies, the genus does not resolve within the western Pacific clade of Areceae, despite its distribution (Norup et al. 2006, Baker et al. in prep.). Lewis and Doyle (2002) resolve Hydriastele as sister to the western Pacific clade. (J. Dransfield & N. Uhl & C. Asmussen & W.J. Baker & M. Harley & C. Lewis, Genera Palmarum. The evolution and classification of palms. 2008)

Taxonomic accounts

Bibliography

A. J. Dransfield & N. Uhl & C. Asmussen & W.J. Baker & M. Harley & C. Lewis, Genera Palmarum. The evolution and classification of palms. 2008
B. World Checklist of Arecaceae