Benstonea Callm. & Buerki

Callmander, Martin W., Lowry Ii, Porter P., Forest, Félix, Devey, Dion S., Beentje, Henk & Buerki, Sven, 2012, Benstonea Callm. & Buerki (Pandanaceae): characterization, circumscription, and distribution of a new genus of screw-pines, with a synopsis of accepted species, Candollea 67 (2), pp. 323-345 : 328-329

Benstonea Callm. & Buerki , nom. & stat. nov.

≡ Pandanus sect. Acrostigma Kurz in J. Bot. 5: 100. 1867. ≡ Pandanus subg. Acrostigma (Kurz) B. C. Stone in Bot. Jahrb. Syst. 94: 521. 1974 [non Acrostigma O. F. Cook & Doyle (Arecaceae) in Contr. U.S. Natl. Herb. 16: 228. 1913].

Type: Benstonea affinis (Kurz) Callm. & Buerki (≡ Pandanus affinis Kurz ) (lectotype designated by ST. JOHN 1960 : 226).

Acaulescent or short-stemmed shrubs, often epiphytic, rarely tall trees. Leaves ligulate to linear-attenuate; leaf apex adaxially spinulose along the two main pleats (spines rarely absent). Inflorescences terminal or lateral on short side-branches, pistillate cephalia solitary, sometimes spicately disposed. Cephalia always of simple drupes, drupes never connate into phalanges; pileus usually distinct and calyptrate, grading upward into a hard, spiniform style; stigma linear, always positioned on abaxial side of the style. Endocarp usually with seed-chamber roofed by a thin cartilaginous partition above which is located a small more or less distinct supra-seminal chamber distinct from the rest of the apical mesocarp. Staminate inflorescence normally spicate. Staminate flowers sessile, composed of free stamens with anthers much longer than the short or nearly obsolete filaments, apiculate, sometimes stamens arranged in pauci-staminate dyads, phalanges or triads.

Etymology.– This genus is named in honour of Benjamin Clemens Stone (1933-1994) to whom we dedicate this article. Ben contributed immensely to the taxonomy of Pandanaceae and was the leading authority on the family for several decades; his work will remain fundamental to the study of the group for many years to come.

Observations. – As suggested above, our current understanding of relationships indicates that the entity recognized by STONE (1974) as Pandanus subg. Acrostigma is probably not monophyletic, and that the group treated here as Benstonea should be limited to include only the members historically assigned to Pandanus sect. Acrostigma (excluding P.microglottis ), along with two clearly related species originally placed in sect. Fusiforma ( P.pachyphyllus and P. biplicatus ). The other species assigned to Pandanus subg. Acrostigma by STONE (1974), viz. the members of sects. Epiphytica and Pseudoacrostigma, along with the remaining species of sect. Fusiforma, are morphologically distinct and currently remain in Pandanus (as redefined here), although their taxonomic affinities within the family remain to be elucidated.

Benstonea is the third largest genus of Pandanaceae , with 50 currently accepted species (see below). It ranges from India to Australia with its centre of diversity in Borneo (21 spp. [17 of which are endemic]) and Peninsular Malaysia (14 spp. [6 endemic]), where two third of the species are found ( Fig. 3 ). Most members of the genus are acaulescent or shortstemmed shrubs, or facultative or true epiphytes, rarely tall trees [e.g. B. atrocarpus (Griff.) Callm. & Buerki ]. Species occur in a variety of habitats including lowland rainforest, swamps, mangrove fringes and montane forests on various soil types (granitic, sandstone and limestone) ( STONE, 1978). Benstonea can be easily recognized in the field by its: 1) staminate flowers bearing single (sometimes 2 or 3 connate) stamens with a short filament and a narrow anther; and 2) pistillate drupes always monocarpellate, with a sharp spiniform style and an abaxial stigmatic groove ( Figs. 4-6 ). When fertile, the only taxa with which Benstonea can possibly be confused are some species of Pandanus sect. Solmsia B. C. Stone from subg. Rykia (de Vriese) B. C. Stone , which also bear simple spiniform styles, but which have a stigmatic groove that is always adaxial on the style. The presence of teeth along the two ventral pleats of the leaf apex can also help to recognize Benstonea when sterile, although some Pandanus species found in regions where Benstonea is present (i.e. Pandanus echinodermos Holttum & H. St. John and P.pentodon Ridl. , both occurring in Peninsular Malaysia) also bear ventral apical teeth ( STONE, 1968a).

Figures

Fig. 3. – Distribution map of Benstonea Callm. & Buerki showing the number of species and the level of endemicity per geographical region.

Fig. 4. – Infructescences and details of stigmas of species of Benstonea Callm. & Buerki. A. Benstonea affinis (Kurz) Callm. & Buerki; B. Benstonea gibbsiana (Martelli) Callm. & Buerki; C. Benstonea ornata (Solms) Callm. & Buerki; D. Benstonea pachyphylla (Merr.) Callm. & Buerki. [Photos: M. W. Callmander]

Fig. 5. – Infructescences and details of stigmas of species of Benstonea Callm. & Buerki. A. Benstonea parva (Ridl.) Callm. & Buerki; B. Benstonea pectinata (Martelli) Callm. & Buerki; C. Benstonea rupestris (. C. Stone) Callm. & Buerki; D. Benstonea thomissophylla (. C. Stone) Callm. & Buerki. [Photos: M. W. Callmander]

Fig. 6. – Infructescence of Benstonea thurstonii (C. H. Wright) Callm. & Buerki with details of stigmas in frame. [Photo: M. W. Callmander]