Delonix Raf., Fl. Tellur. 2: 92. 1837.

Figs 67, 68, 70, 77

Aprevalia Baill., Bull. Mens. Soc. Linn. Paris 1: 428. 1884. Type: Aprevalia floribunda Baill. [≡ Delonix floribunda (Baill.) Capuron]

Lemuropisum H. Perrier, Bull. Soc. Bot. France 85: 494. 1939. Type: Lemuropisum edule H. Perrier [≡ Delonix edulis (H. Perrier) Babineau & Bruneau]

Delonix sect. Aprevalia (Baill.) Capuron, Adansonia, n.s. 8(1): 12. 1968. Type: Delonix floribunda (Baill.) Capuron [≡ Aprevalia floribunda Baill.]

Type.

Delonix regia (Bojer ex Hook.) Raf. [≡ Poinciana regia Bojer ex Hook.]

Description.

Shrubs ( D. edule) or small to medium-sized trees to 30 m, often forking low down and forming spreading, flat-topped umbrella crowns (Fig. 67P, Q), or in a subset of species, the trunk fusiform with distinctive 'bottle tree’ growth form constricted at the base, swollen above and only tapering immediately below the rounded crown, reminiscent of baobabs (Fig. 67O); generally unarmed, but in D. edule armed with spinescent shoots. Stipules generally minute or absent, but pinnate or bipinnate in D. regia . Leaves generally bipinnate, 2-13 pairs of pinnae, and (6) 12-20 (40) pairs of leaflets per pinna, much reduced and simply paripinnate in D. edule with just 2-3 pairs of small leaflets. Inflorescences axillary racemes usually produced at several consecutive nodes and flowers generally held above the foliage (Fig. 68Q), pedicels jointed, bracts caducous (or often persistent in D. regia). Flowers bisexual, usually large and showy (Figs 67Q, 68H, I); hypanthium short, turbinate; sepals 5, free, subequal, valvate, strongly reflexed, leathery and thickened especially towards the tips; petals usually 5, these spreading, round or ovate with a long claw, the margins crisped and frilled when fully expanded, somewhat erose or deeply lacerate, the median petal usually larger, differently coloured, and held in front of the other petals, its claw with inrolled margins, forming a narrow funnel containing nectar, petals white, pale pink or bright scarlet ( D. regia), the upper petal with a central yellow and white blotch (Fig. 68I), and the whole petal suffusing red with age or post pollination (Fig. 68H), but in two species the petals much reduced and in D. floribunda (Baill.) Capuron the lateral petals absent and only a single erect, narrow yellow petal is present; stamens 10, free, equal, longer than petals, spreading, not clustered around the ovary, anthers dorsifixed, glabrous; pollen in oblate tricolporate monads with coarsely reticulate surface ornamentation with sinuous, slightly convoluted muri; ovary stipitate, style filiform, stigma small and glabrous or ciliate. Fruits usually large, many-seeded, linear-oblong, somewhat flattened, woody, pendulous or suberect, either long, straight or weakly falcate and strap-like (Fig. 70O) or shorter and tightly curved (Fig. 70N), tardily dehiscent until after they have fallen, eventually splitting into 2 flat (non-twisting) valves, or (in non-Madagascan species) the valves thinner, coriaceous and less robust, and (in D. edule) lacking separate seed chambers, the valves thinner, coriaceous, twisting at dehiscence. Seeds ellipsoidal or subspherical to ovoid, pale brown, finely mottled, in individual chambers or, in D. edule, oblong, truncate, the testa cream-white and leathery.

Chromosome number.

2 n = 26 or 28 (Goldblatt 1981b; Van-Lume and Souza 2018).

Included species and geographic distribution.

Twelve species, ten endemic to south-western, western and northern Madagascar, one widespread in eastern and north-eastern Africa extending to adjacent Arabia, and one restricted to northern Kenya and Somalia (Fig. 77).

Ecology.

Seasonally dry and arid thickets including the spiny dry forests of south-western Madagascar, Acacia - Commiphora woodland in north-eastern Africa, and semi-desert scrub. A few species have distinctive swollen trunks and 'bottle tree’ habits (Fig. 67O). Deciduous, or largely so, often flowering when leafless or as new flush leaves emerge. Pollination is thought to be by moths in the white-flowered species and by Souimanga sunbirds ( Nectarinia) in the yellow and red-flowered species.

Etymology.

From Greek, delo - (= evident, conspicuous) and - onyx (= claw or nail) in reference to the fact that the petals have very long claws.

Human uses.

The well-known Flamboyant or Flame tree, Delonix regia with its magnificent showy racemes of scarlet flowers is a favourite in cultivation as an ornamental street and garden tree throughout the tropics (Lewis 2020a). Less well-known is that the seeds of D. edule (formerly Lemuropisum edule H. Perrier) are eaten when young and have potential as a food crop (Du Puy and Rabevohitra 2002).

Notes.

The genus Delonix is sister to the morphologically similar Colvillea . These two genera together are robustly supported as sister to the clade comprising two monospecific endemic Mexican genera Conzattia and Heteroflorum (Fig. 66; Ringelberg et al. 2022), providing a striking example of trans-continental phylogenetic biome conservatism to seasonally dry and arid tropical climates (Ringelberg et al. 2020). The monospecific genus Lemuropisum was found to be nested within Delonix and sunk within that genus by Babineau and Bruneau (2017), adding further to the already considerable heterogeneity of flower and fruit morphology in the genus. The inflorescences of Delonix although superficially resembling those of Peltophorum, Bussea and Colvillea with the flowers generally held above the foliage, never form a true terminal panicle, but are rather axillary racemes usually produced at several consecutive nodes.

Taxonomic references.

Babineau and Bruneau (2017); Brenan (1967), with illustration; Du Puy and Rabevohitra (2002), with illustration; Du Puy et al. (1995), with illustration; Lewis (2020a), with illustration.