Acrocarpus Wight ex Arn., Mag. Zool. Bot. 2(12): 547. 1839.

Figs 7, 10

Type.

Acrocarpus fraxinifolius Wight & Arn.

Description.

Unarmed evergreen tree, bark pale grey, smooth, brachyblasts absent. Stipules not seen, presumed lacking, at least on mature leaves. Leaves large, bipinnate with a single terminal pinna, leaflets ovate-lanceolate, acuminate (Fig. 7E). Inflorescences densely flowered, erect, or drooping racemes, or panicles (Fig. 7C). Flowers bisexual, patent or nodding, 5-merous, sepals and petals green, sepals slightly imbricate, petals slightly longer; disk cupular, completely united with the red hypanthium; androecium haplostemonous, stamens five, exserted from corolla (Fig. 7C), filaments with basal half green, upper half orange-red, anthers dorsifixed, with introse slits; pollen with a scabrate-punctate sculpture pattern; ovary stipitate, the short style tapered and inflexed to a minute stigmatic pad. Fruits linear to linear-oblong, dehiscent, 2-valved, narrowly winged along upper suture, several- to many-seeded (Fig. 7D). Seeds ovate or circular, compressed, testa surface with concentric fracture lines, pleurogram lacking.

Chromosome number.

2 n = 24 (Goldblatt 1981b).

Included species and geographic distribution.

Monospecific ( A. fraxinifolius), native to South East Asia (from the Indian subcontinent to China and Indo-China) (Fig. 10).

Ecology.

Tropical and subtropical broad-leaved rainforest and evergreen gallery forest.

Etymology.

From Greek, acro - (= summit or top) and carpos (= fruit), most probably alluding to the long-stipitate ovaries and fruits.

Human uses.

Timber of A. fraxinifolius (pink cedar tree) is used to make tea boxes, furniture, and plywood; the species is widely grown as an ornamental and is also used for fodder, gums, and bee forage (for honey) (Lewis 2005b).

Notes.

Acrocarpus was earlier placed in its own Acrocarpus group of tribe Caesalpinieae (Polhill and Vidal 1981), but the first molecular phylogenetic analyses based on just a few plastid markers (Doyle et al. 2000; Bruneau et al. 2001; Kajita et al. 2001) suggested the genus was closely related to Ceratonia (then placed in Cassieae), a relationship that clearly is supported in the phylogenomic analyses of Ringelberg et al. (2022). A large range of flower size throughout its distribution range formerly led to the recognition of two species.

Taxonomic references.

Hou (1996a); Lewis (2005b).