Oncocalamus (G.Mann & H.Wendl.) H.Wendl., Palmiers : 252 (1878)

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Content

Distribution

Map uses TDWG level 3 distributions (https://github.com/tdwg/wgsrpd)

Angola present (World Checklist of Arecaceae)C

Benin present (World Checklist of Arecaceae)C

Cabinda present (World Checklist of Arecaceae)C

Cameroon present (World Checklist of Arecaceae)C

Chad present (World Checklist of Arecaceae)C

Congo present (World Checklist of Arecaceae)C

Equatorial Guinea present (World Checklist of Arecaceae)C

Gabon present (World Checklist of Arecaceae)C

Nigeria present (World Checklist of Arecaceae)C

Zaire present (World Checklist of Arecaceae)C

Five species described from equatorial West Africa and the Congo Basin. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Oncocalamus has a distinct Guineo-Congolian distribution and ranges from SE Nigeria to northern Angola, predominantly in coastal forest. (Sunderland, T.C.H. 2012: A taxonomic revision of the rattans of Africa (Arecaceae: Calamoideae). – Phytotaxa 51: 1-76)B

Discussion

The strange flower cluster of Oncocalamus is unique, not only in the subfamily but within the whole family. Vegetatively, Oncocalamus is very similar to Eremospatha and Laccosperma. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A
Recent collections have provided considerable insight into the life history and morphology of this intriguing genus. Although recent literature has stated that Oncocalamus is represented by only one, very variable, species, O. mannii, there are in fact four species present in Africa. (Sunderland, T.C.H. 2012: A taxonomic revision of the rattans of Africa (Arecaceae: Calamoideae). – Phytotaxa 51: 1-76)B

Diagnosis

Clustering high-climbing pinnate-leaved rattan palms of Equatorial West Africa; sheaths armed with detachable spines; pleonanthic and monoecious, the flowers are borne in paired cincinni within conspicuous bracts, the basal 1–few pistillate, the others staminate, an arrangement unique in the family. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Biology And Ecology

Confined to lowlying tropical rain forest. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Common Name

Common names numerous (Sunderland 2001). (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Etymology

Onkos — hook, calamus — reed, but no explanation was given for the derivation. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A
(Greek) onkos = hook and calamus = reed. (Sunderland, T.C.H. 2012: A taxonomic revision of the rattans of Africa (Arecaceae: Calamoideae). – Phytotaxa 51: 1-76)B

Uses

No local uses have been specifically recorded but the stems are probably used as a source of cane. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Description

Clustered, spiny, high-climbing, pleonanthic, monoecious, rattan palms. Stem eventually becoming bare, circular in cross-section, with long internodes. Leaves pinnate, bifid in juveniles, with a terminal cirrus; sheath strictly tubular, bearing scattered, black, bulbous-based, triangular, brittle spines and scattered, thin, caducous indumentum; ocrea conspicuous, tightly sheathing, neatly truncate, armed as the sheath; knee absent; petiole present but usually very short, absent in mature flowering stems; rachis armed with scattered spines as the leaf sheath; cirrus bearing neat pairs of reflexed acanthophylls; leaflets few to numerous, usually single-fold, sometimes with 2 or more folds, entire, acute, linear, lanceolate or somewhat sigmoid, regularly arranged, usually armed along the thickened margins with robust spines, midribs evident, other large veins rather distant, transverse veinlets conspicuous; proximal few leaflets sometimes smaller than the rest, heavily armed and reflexed across the sheathed stem. Inflorescences branched to 1 order; peduncle enclosed within the leaf sheath and emerging from its mouth, ± hemispherical in cross-section; prophyll tubular, tightly sheathing, 2-keeled, 2-lobed at its tip, much shorter than the sheath; peduncular bracts ca. 4, ± distichous, tightly sheathing at first, later splitting longitudinally, each with a short triangular lobe; rachis longer than the peduncle; rachis bracts like the peduncular, rather close; first-order branches pendulous or spreading with a basal 2-keeled tubular prophyll and numerous distichous, short, tubular, somewhat inflated, striate bracts, each enclosing a flower cluster, after anthesis eventually irregularly splitting and tattering; flower cluster partially covered by a tubular 2-keeled prophyll and consisting of up to 11 flowers arranged in a group with a central 1 or 3 pistillate flowers and 2 lateral cincinni of 2–4 staminate flowers, each flower, apart from the central pistillate bearing an open, spathulate, 2-keeled, prophyllar bracteole (the precise arrangement of the flowers not yet understood). Staminate flowers symmetrical; calyx membranous, striate basally, stalked, tubular, with 3 short triangular, apiculate lobes; corolla apparently only slightly exceeding the calyx, divided almost to the base into 3 elongate, striate, valvate petals; stamens 6, filaments united to form a thick, fleshy androecial tube, free from the corolla, tipped with 6 shallow lobes, bearing pendulous, rounded, latrorse anthers on the inside; pistillode very narrow, conical, slightly exceeding the androecial tube. Pollen ellipsoidal, bi-symmetric; aperture a distal sulcus; ectexine tectate, very finely perforate, interspersed with very small spinulae, aperture margin similar; infratectum columellate; longest axis 23–29 µm [1/4]. Pistillate flowers superficially very similar to the staminate except slightly broader; the calyx and corolla similar; staminodal tube bearing minute empty anthers; gynoecium tricarpellate, triovulate, ± ellipsoidal, covered in reflexed scales, style long, narrow, 3-angled, ovule form unknown. Fruit ± spherical, stigmatic remains minute, conical, apical; epicarp covered in vertical rows of rather thin reflexed scales, mesocarp very thin, almost obsolescent at maturity, endocarp not differentiated. Seed single, basally attached with an oval hilum, covered with a ?thick sarcotesta and endosperm homogeneous, laterally deeply penetrated by a smooth-margined mass of inner seed coat; embryo lateral opposite the intrusion. Germination and eophyll unknown. Cytology not studied. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A
Clustered, spiny, moderate to high-climbing, pleonanthic, monoecious rattan palms. Stem circular in cross section, with short to medium internodes; sucker shoots axillary. Leaves pinnate, strongly bifid in juveniles, with a terminal cirrus; sheath strictly tubular, bearing scattered, brown or black, bulbous-based triangular, brittle spines, sometimes becoming bare, and scattered, thin, white, caducous indumentum; ocrea conspicuous, tightly sheathing, neatly horizontally truncate, lobed or somewhat saddle-shaped, armed as the sheath, spines often concentrated on ocrea margin; knee absent, although rounded horizontal swelling visible at the base of the leaf in some species; leaves sessile, or with a very short flattened petiole; rachis unarmed or sparsely to profusely armed on the underside; cirrus bearing reflexed acanthophylls; elaminate rachis co mmon on lower part of stems, bearing equidistant, alternate to opposite acanthophylls; spear leaf deep orange to bright crimson to light green; leaflets few to numerous, usually single-fold, sometimes with 2-4 folds, entire, acute, linear, lanceolate or sigmoid, regularly arranged, usually armed along the thickened margins with robust spines, less so distally, midribs evident, other large veins rather distant, transverse veinlets conspicuous, proximal few leaflets smaller than the rest, often erect, vertical to rachis and stiffly swept back across stem or arching and somewhat pendulous. Inflorescences produced in axils; peduncle enclosed within the leaf sheath and emerging from its mouth, hemisperical or flattened and rectangular in cross-section; prophyll tubular, tightly sheathing, 2-keeled, 2-lobed at its tip, much shorter than the sheath; peduncular bracts ca.4, ± distichous, tightly sheathing at first, later splitting longitudinally, each with a short triangular or straight lobe; rachis longer than the peduncle; rachis bracts like the peduncular, rather close; rachillae pendulous with a basal 2-keeled tubular prophyll and numerous distichous, short, tubular, somewhat inflated, striate bracts, each enclosing a flower cluster, eventually longitudinally splitting and tattering post anthesis; flower cluster partially covered by a tubular 2-keeled prophyll and consisting of 5, 7, 9 or 11 flowers arranged in a group; 1-3 pistillate flowers in the centre subtended by 2 lateral cincinni of 0-2 pistillate and 2-4 staminate flowers, each flower, apart from the central pistillate, bearing an open, spathulate, 2-keeled, prophyllar bracteole. Staminate flowers symmetrical; calyx membranous, striate basally, stalked, tubular, with 3, short, triangular, apiculate lobes; corolla enclosed or only slightly exceeding the calyx, divided almost to the base into 3, elongate, striate, valvate petals; stamens 6, filaments united to form a thick fleshy, androecial tube, free from the corolla, tipped with 6 shallow lobes, bearing pendulous, rounded, latrorse anthers on the inside; pollen elliptic, monosulcate, with scabrate, tectate exine; pistillode very narrow, conical, slightly exceeding the androecial tube. Pistillate flowers superficially very similar to the staminate except slightly broader; calyx and corolla similar; staminodial tube bearing tiny empty anthers; gynoecium tricarpellate, triovulate, ± ellipsoidal, covered in reflexed scales, style long, narrow, 3-angled; ovule basally attached, anatropous. Fruit ± spherical, stigmatic remains minute, conical; epicarp covered in vertical rows of rather thin reflexed scales, mesocarp very thin, almost obsolescent at maturity, endocarp not differentiated. Seed single, ± rounded, smooth or warty, basally attached with an oval hilum, covered with a thin, papery, sweet sarcotesta; endosperm homogenous, laterally penetrated by a smooth-margined mass of inner seed coat; embryo lateral opposite the intrusion. Germination adjacent-ligular; eophyll bifid, petiole of seedling dull reddish pink. (Sunderland, T.C.H. 2012: A taxonomic revision of the rattans of Africa (Arecaceae: Calamoideae). – Phytotaxa 51: 1-76)B

Anatomy

Not studied. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Fossil record

No generic records found. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Relationships

The monophyly of Oncocalamus has not been tested. The genus resolves as sister to a clade of Eremospatha and Laccosperma with moderate support (Baker et al. 2000a, 2000b, Asmussen et al. 2006). (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Taxonomic accounts

Sunderland (2001, 2007). (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Bibliography

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

B. Sunderland, T.C.H. 2012: A taxonomic revision of the rattans of Africa (Arecaceae: Calamoideae). – Phytotaxa 51: 1-76

C. World Checklist of Arecaceae

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