Areca rheophytica J.Dransf., Kew Bull. 39: 18 (1984)

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Distribution

Map uses TDWG level 3 distributions (http://www.nhm.ac.uk/hosted_sites/tdwg/geogrphy.html)
Borneopresent (World Checklist of Arecaceae)A

Discussion

  • The relationships of the rheophytic Areca of Sabah are clearly with hexandrous species of Arecella (in Furtado's sense); it seems closest to A. hutchin- soniana and A. vidaliana of the Philippines. A. hutchinsoniana does not have rheomorphic unicostate leaflets and so is easily distinguished. A. vidaliana on the other hand is much more difficult to separate, and I had originally thought the Sabah taxon was conspecific with it. Beccari (1907) described two closely related species from Palawan - A. vidaliana with broad leaflets, and A. mammillata with unicostate leaflets. Later (1919) he sank the latter into the former, having noted how variable is the leaf dissection in Areca. Merrill (1922) for no apparent reason cited A. vidaliana as a synonym of A. mammillata rather than vice versa. In 1979 I had the opportunity to see A. vidaliana in the field in Palawan. Near Puerto Princesa it grows in small crown forest rich in bamboo (Schizostachyum sp.) developed on serpentine rock, and occurs in a variety of forms ranging from unicostate to broad- costate. In habitat and aspect it is very different from the Sabah rheophyte. It is worth stressing that there was no rheophytic Areca sp. in the area I visited, though the habitat was abundant. Although I have found difficulty in separating what are geographically and ecologically distinct taxa, I still believe the Sabah taxon is sufficiently distinct to be accorded specific status. At present, true A. vidaliana is known from Malaysian territory only from P. Balembangan between the coast of Sabah and Palawan.
    A. rheophytica is a most elegant species. Professor van Steenis wrote to me in relation to the preparation of his book on rheophytes (van Steenis 1981) concerning this taxon. At the time I had not seen it in the field, and as I assumed it to be non-rheophytic A. vidaliana the taxon was not included by Professor van Steenis. (J. Dransfield, The genus Areca (Palmae: Arecoideae) in Borneo. 1984)B

Diagnosis

  • elegantissima, rheophytica, in ripis fluminum rivulorumque per petras serpentinas fluentium crescens, ad sectionem Arecellam (sensu Furtado) pertinens, a ceteris speciebus Borneen- sibus habitatione et foliolis plicarum singularium approximatis compositis, regulatim dispositis bene distincta; staminibus 6 et habitu solitario A. hutchinsonianae et A. vidalianae insularum Philippinarum affinis et vero a formis A. vidalianae quae foliola plicarum singularium composita habent, haud disting- uibilis, sed floribus pistillatis angustissimis, caule glabrato, habitatione et aspectu differt. (J. Dransfield, The genus Areca (Palmae: Arecoideae) in Borneo. 1984)B

Biology And Ecology

Description

  • Solitary, short-stemmed, rheophytic, undergrowth palm, Stem to c. 2 m tall, usually less, 1-2 cm diam., pale brown except near the crownshaft where green, glabrous, internodes 2-4 cm, the nodal scars conspicuous c. 3-5 mm high. Crownshaft usually swollen, 15-30 x 2-4 cm, pale green. Leaves c. 7-8 in the crown; sheaths to 25 cm, usually less, smooth when fresh, drying ridged, bearing very sparse scattered scales; petiole 8-15 x 0.3-0.5 cm, channelled adaxially, rounded abaxially, bearing very sparse brown scales; leaflets 12-22 on each side of the rachis, dark green, close, regularly arranged, all single-fold except the apical pair and sometimes the basal pair which are 2-3-ribbed, concolorous, bearing very sparse, minute, brown scales scattered on both surfaces. Inflorescence erect at anthesis, to 22 cm, often less; prophyll to 25 x 3.5 cm, conspicuously winged, the wing margins somewhat erose and hairy towards the tip, the prophyll surface striate on drying, bearing scattered brown scales; peduncle 7-15 x 5 mm, winged at the very base; axis branching to 3 orders; rachillae slender, very numerous, to 120 x 1 mm, sometimes with a short bare portion at the base, usually with a basal triad, rarely with several triads, otherwise bearing paired staminate flowers in a single row on one side. Staminate flower narrow-ovoid, trigonous, creamy-white, citrus-scented; sepals 3, free, triangular, keeled, c. 0.8 x 0.4 mm; petals 3, striate, narrow-triangular, c. 2.2 x 0.7 mm; stamens 6, filaments very short, anthers elongate, c. 1.4 x 0.3 mm; pistillode trifid, conspicuous, exceeding the stamens, c. 1-8 X 0-3 mm. Pistillate flower at anthesis narrow, trigonous, c. 11 x 3 mm; sepals 3, free, imbricate, c. 7 x 4 mm; petals 3, exceeding the sepals, c. 10 x 6 mm, imbricate, with short triangular, valvate tips; ovary fusiform, c. 10 x 3 mm, tipped with 3 short stigmas. Fruit fusiform, pale green at first, at maturity becoming cherry-red, narrow-ellipsoidal, c. 20 x 7 mm; mesocarp becoming < 2-5 mm thick; seed fusiform, c. 15 x 5 mm. (J. Dransfield, The genus Areca (Palmae: Arecoideae) in Borneo. 1984)B

Materials Examined