Leonardoxa africana subsp. gracilicaulis, McKey, 2000

Mckey, Doyle B., 2000, Leonardoxa africana (Leguminosae: Caesalpinioideae): a complex of mostly allopatric subspecies, Adansonia (3) 22 (1), pp. 71-109 : 102-103

Leonardoxa africana subsp. gracilicaulis

McKey, subsp. nov. (= group 1)

Haec subspecies Leonardoxae africanae subsp. rumpiensi arcte atque L. africanae subsp. letouzeyi et subsp. africanae nonnihil remotior affinis, sed ab ea glandulis nectariferis crateriformibus ad foliola proximalia nullis ad duabus atque foliorum expansione simultanea ramunculi ad nodos terminales duos ad quattuor, ab omnibus ramunculorum juvenilium internodiis non inflatis atque racemis ad ramunculos diametro 5-10 mm axillaribus distinguitur.

TYPUS. — Letouzey 10201, Cameroon, Southern Province , Colline Ongongondje near Akonekye, 15 km NW Ambam, ca. 700 m, 23 Mar. 1970 (holo-, P; iso-, BR, K, WAG, YA).

Tree to 25 m tall. Trunk up to 50-60 cm diam. Young shoots produced in flushes of (1-)2-4 internodes and leaves at each branch tip; internodes of young twigs (1.1-)3.7(-7) cm long, not modified as myrmecodomatia, not swollen; twigs (2-)2.3(-3.1) mm diam. at apex tapering to ca. 1- 2 mm diam. at base of internode. Prostoma lacking. Leaves 2-3-jugate; leaflets elliptic, falcate, apex acuminate to long-acuminate, the smallest ones (proximal pair) (9.6-)10.9(-15) cm long and (3-)4(-5) cm broad, largest ones (the distal ones in 2-jugate leaves, median ones in 3-jugate leaves) (12-)15(-26) cm long and (4-)5.5(-9.5) cm broad. Nectary glands small (smooth gland surface oblong, about 0.5 × 0.75 mm), mostly restricted to proximal leaflets, where they are variable in number (0-2). Racemes very short (axis to 3 cm long), with 25-40 flowers, axillary on small twigs of 2-3 (rarely 5-10) mm diam. ( Fig. 8 ). Flowers 1.6-1.8 cm in diam; pedicels 2-4 mm long; calyx white to pale lilac, sepals 0.5-0.8 cm long; petals lilac to violet, 0.6-1 cm long. Ovules 4-5. Fruit oblong-obovate, ca. 10 cm long, 4 cm broad.

Leonardoxa africana subsp. gracilicaulis is distinguished from the three other subspecies of the L. africana complex by the absence of swollen internodes and prostoma (the subspecies gracilicaulis is not a myrmecophyte: Fig. 6A ). Foliar nectary glands are present, but are smaller than those of the myrmecophytic subspecies ( Fig. 5A ). This subspecies also differs from the others in floral characters. Flowers are white and lilac in colour, rather than pink or red, the most frequent colours in the myrmecophytes. Also, inflorescences are usually axillary on small twigs in this subspecies ( Fig. 8A ). Cauliflory is very frequent in the myrmecophytes, but in field populations and herbarium specimens studied by us, cauliflory has been recorded in the non-myrmecophytic subspecies only at the summit of Nta Ali ( Table 6), in a population that may be affected by hybridisation with L. africana subsp. letouzeyi (see below). Trees of this subspecies, especially in hilltop (piedmont and lower submontane) habitats where it is most common, reach larger size than is ever attained by any of the myrmecophytes.

DISTRIBUTION. — This subspecies includes all the specimens collected from Gabon, Equatorial Guinea, and southern Cameroon from the vicinity of Yaoundé southward and east of the coastal plain ( Fig. 4 ). In southern Cameroon, this subspecies is characteristically abundant on summits of hills, such as Nkolebengue ( THOMAS & THOMAS 1993) and Zingui (this study). Near Yaoundé, L. africana subsp. gracilicaulis is one of the most frequent trees in submontane forest from 1,000 m elevation upwards ( ACHOUNDONG 1985, 1996). The nonmyrmecophytic L. africana abundant in forest on the summit of Nta Ali ( ACHOUNDONG 1995) are also tentatively ascribed to this subspecies.This subspecies is much less frequent in lowland forests, where it is highly localised along streams and patchily distributed. (Within its range, lowland habitats are less constantly humid than hilltop and submontane habitats.) In the coastal plain, where the highly specialised myrmecophyte L. africana subsp. africana predominates (see below), L. africana subsp. gracilicaulis has been collected from two inselbergs (Colline Ngwon, 38 km E of Kribi: Letouzey 9371; Nkoltsia, 35 km from the coast, Villiers 807). Near the latter site, it also occurs in lowland forest, near the village Nkoloboundé along the stream Bounde, where it occurs together, interspersed in the same forests, with the specialised myrmecophyte L. africana subsp. africana . This is so far the only site where the two are known to cooccur.In forest along two other streams nearby,only L. africana subsp. africana was present. The two subspecies may co-occur elsewhere, though. The collection Mpom 303, from 14 km SE of Douala on the old Douala-Edea road, includes sheets of

Figures

Fig. 8. — Variation in floral traits within the Leonardoxa africana complex. Bar = 2 cm in both photos. A, inflorescence axillary on a young twig (vertical object just behind the inflorescence) in L. africana subsp. gracilicaulis (Mbalmayo site); hypanthium white, corolla and filaments of stamens lilac, anthers yellow. B, trunciflorous inflorescences in L. africana subsp. africana (Grand Zambi); hypanthium and corolla pink.

Fig. 6. — Internodes of the Leonardoxa africana complex, showing variation in specialisations for housing ants. Bar = 2 cm in all photos. A, apex of internode (note point of attachment of the paripinnately compound leaf) of L. africana subsp. gracilicaulis (Mbalmayo site), showing absence of swelling in this non-myrmecophytic subspecies; B, longitudinal section of internode of L. africana subsp. africana (Bombé Bakundu site) showing the strongly swollen ant-domatium, which in this subspecies is a single internode long.— C and D, prostoma of two myrmecophytic subspecies, located in both cases at the apex of the internode opposite the point of leaf insertion; the diagonally cut structure at the top of each photo is the leaf rachis: C, circular prostoma of L. africana subsp. letouzeyi (Rengo Rock site); prostoma of L. africana subsp. rumpiensis (not shown) is roughly similar in size and shape; D, elongate prostoma of L. africana subsp. africana (Bombé Bakundu site). Both are on internodes produced by plants growing in a greenhouse at the University of Miami, on cuttings uninhabited by ants. The structures are not holes, but are scars produced by the spontaneous drying of the unlignified prostoma in mature internodes.

Fig. 5. — Foliar nectaries of the Leonardoxa africana complex, all shown at the same scale: A, L. africana subsp. gracilicaulis (Zingui hill site); B, L. africana subsp. rumpiensis (Dikomé Balué site); C, L. africana subsp. africana (Akanga site). Nectaries of L. africana subsp. letouzeyi (not pictured) are similar in size to those of subsp. rumpiensis.

Fig. 4. — Geographic distribution of herbarium collections of the Leonardoxa africana complex examined in this study: L. africana subsp. gracilicaulis = Group 1; L. africana subsp. rumpiensis = Group 2; L. africana subsp. letouzeyi = Group 3; L. africana subsp. africana = Group 4.