Calamus longipinna (Arecaceae: Calamoideae) and Its Relatives in New Guinea

Abstract

Summary. The taxonomy and morphology of the Calamus longipinna (Arecaceae) group is revised and discussed. This group of rattan species from New Guinea and the Solomon Islands is defined by the possession of a distinctive, inflated ocrea at the mouth of the leaf sheath and rather uniform A striking feature of the New Guinea species of the rattan genus Calamus is the frequent presence of elaborate ocreas. The ocrea is widespread in some other rattan genera, namely Korthalsia, Plectocomiopsis, Laccosperma, Eremospatha and Oncocalamus. In most cases, the structure is merely a low, inconspicuous, tubular extension of the leaf sheath above the insertion of the petiole. However, in some species of Calamus, Korthalsia and Laccosperma, the ocrea is enlarged, highly conspicuous and widely variable in morphology. For example, some ocreas are inflated and clasp the stem or diverge from it at an acute angle. Ants often colonise inflated ocreas, cultivating scale insects for honeydew on the leaf sheaths and aggressively defending their home, and, at the same time, the rattan (Dransfield 1979). In a few species of Korthalsia and one species of Calamus, the ocrea consists of a reticulum of fibres which is tightly adpressed to the sheath or else expands into an open funnel. A number of Calamus species (e.g. C. paspalanthus Becc. in west Malesia and C. zebrinus Becc. in New Guinea) possess greatly enlarged ocreas, sometimes as long as 1 m or more, that disintegrate and fall not long after emergence. Approximately 14 species of Calamus in New Guinea possess such enlarged ocreas. The C. longipinna Lauterb. & K. Schum. group, the subject of this paper, is characterised by its inflated ocreas that clasp the stem and a characteristic yet rather simple flagelliform inflorescence morphology. The group is distinguished from the ocreate species related to C. macrochlamys Becc. and C. zebrinus Becc. because it does not possess the unusual floral cluster architecture that is so remarkable in this group (Dransfield & Baker, submitted). Calamus humboldtianus Becc. is not included in the C. longipinna group because it bears bizarre inflorescences with congested branches as well as unusual leaf and ocrea morphology. The fibrous, fragile ocrea and robust rachillae of C. klossii Ridl. set it apart from other New Guinea ocreate rattans. Calamus distentus Burret may yet prove to be a relative of the C. longipinna group, but the ocrea diverging from the stem and very slender inflorescence morphology are not congruent with such a placement.