Introduction

The genus Pleuroridgea Tiegh. is the result of revision of generic concepts in the Ochnaceae, in which he split the family into 53 genera, of which 46 were described as new (Van Tieghem, 1902). Among these, Pleuroridgea was defined by the orientation of the cotyledons that are laterally-disposed and by the non-laciniate stipules (Van Tieghem, 1902). Delimited in this way, the genus originally comprised 5 species from Central and East Africa, while Brackenridgea A. Gray was restricted to nine species from south-east Asia and the south Pacific islands.

Despite the fact that Perrier De La Bâthie (1941) stated Pleuroridgea to be morphologically very similar to the genus Brackenridgea A. Gray, he maintained the genus adding two new Malagasy species: Pleuroridgea madecassa H. Perrier and P. tetramera H. Perrier.

However, the differences between the African and the Asian species have not been considered sufficient to merit separation at the generic level, and the genus Pleuroridgea has not generally been accepted (for example, Gilg, 1925). The five species placed there by van Tieghem are now consistently referred to Brackenridgea by authors working on African floras (four are treated as synonyms of a broadly circumscribed B. zanguebarica Oliv.). Robson (1962) summarized the distinguishing characters of the three genera of Ochnaceae present in the “Flora Zambesiaca” region (Brackenridgea, Ochna L. and Ouratea Aubl.) noting that Brackenridgea was distinguished by: “a lobed ovary with gynobasic style and a fruit with several separate 1-seeded drupelets borne on the more of less enlarged receptacle”. Robson's point of view has been followed in other floras for Africa (Dutoit & Obermeyer, 1976; Verdcourt, 2005). Furthermore Dutoit & Obermeyer (1976) specifically included the Malagasy species in their count of four species present in “tropical and subtropical Africa and Madagascar”, without mentioning any details or providing the needed new combinations. We confirm that the Malagasy species are comfortably encompassed by the current circumscription of Brackenridgea, concurring with Schatz (2001) who included Brackenridgea in his generic key to Ochnaceae in Madagascar.

This note serves to (1) formally transfer the two Malagasy endemic Pleuroridgea species to Brackenridgea; (2) lectotypify the two species that were validly described by Perrier De La Bâthie (1941) with multiple syntypes. It has been prepared within the context of Missouri Botanical Garden's “Catalogue of Vascular Plants of Madagascar project”, which aims to disseminate up-to-date information on-line ( www.efloras.org/madagascar) and in printed media.

Taxonomy and nomenclature of the Malagasy species of Brackenridgea

The genus Brackenridgea comprises ca. 12 species distributed from Africa to the Fiji Island (Schatz, 2001). Two species are endemic to Africa: B. arenaria (De Wild. & T. Durand) N. Robson (Central Africa) and B. zanzibarica (East Africa). A third species from Tanzania (Mafia Island) probably merits description (Verdcourt, 2005). The remaining species occur in South-East Asia (Andaman Island, Malaysia, Philippines to New Guinea) to Southern Pacific (Fiji) and Australia (Queensland) (Kanis, 1968). We have reviewed the available material referred to Pleuroridgea by Perrier De La Bâthie (1941) and specimens which have been collected subsequently to evaluate species level taxonomy. This review confirms the presence in Madagascar of two endemic species:

Brackenridgea madecassa (H. Perrier) Callm., comb. nova

Pleuroridgea madecassa H. Perrier in Notul. Syst. (Paris) 10: 37. 1941.

Lectotypus (designated here): Madagascar. Prov. Antsiranana: Mt Ambohipiraka, [13°10′30″S 46°06′00″E], 10.1932, fl. Perrier de la Bâthie 18759 (lecto-: P [P00048463]!; iso-: P [P00048464, P00048465]!).

Conservation status. — With an EOO of 162 244 km², an AOO of 36 km² and 11 subpopulations, even though none are situated within the protected area network, B. madecassa is assigned a preliminary status of “Least Concern” (LC) following the IUCN Red List Categories and Criteria (IUCN, 2010) (calculation following Callmander & al., 2007).

Observations. — Brackenridgea madecassa can be recognised by its pentamerous flowers; short (2 mm) style; 5–10 carpels and 13–20 stamens (Perrier De La Bâthie, 1941). Brackenridgea madecassa is widespread in Madagascar growing in dry to humid forests.

Brackenridgea tetramera (H. Perrier) Callm., comb. nova

Pleuroridgea tetramera H. Perrier in Notul. Syst. (Paris) 10: 38. 1941.

Lectotypus (designated here): Madagascar. Prov. Toliara: Vallée moyenne du Mandrare, près d'Anadabolava, Mt Vohitrotsy, 700–800 m., [24°12′40″S 49°19′00″E], 12.1933, fl., Humbert 12687 (lecto-: P [P00048 4668]!; isolecto-: G [G00006139]!, P [P000484666, P000484667]!).

Conservation status. — With only two collections known, both collected by Henri Humbert near Anadabolava in the Mandrare valley dating back to December 1933, an EOO of 9 km², one subpopulation not in the protected area network, B. tetramera is assigned a preliminary status of “Critically Endangered” (CR A3c; B2ab[iii]) following the IUCN Red List Categories and Criteria (IUCN, 2001) (calculation following Callmander & al., 2007).

Observations. — Brackenridgea tetramera can be recognised by its tetramerous flowers; long (8 mm) style; 3–4 carpels and 8–10 stamens (Perrier De La Bâthie, 1941). The species grows in southwestern Madagascar in the sub-arid bush.