Leonardoxa africana subsp. rumpiensis McKey, 2000

Mckey, Doyle B., 2000, Leonardoxa africana (Leguminosae: Caesalpinioideae): a complex of mostly allopatric subspecies, Adansonia (3) 22 (1), pp. 71-109 : 101-102

3. Leonardoxa africana subsp. rumpiensis McKey , subsp. nov. (= group 2)

Haec subspecies Leonardoxae africanae subsp. letouzeyi perarcte affinis, sed ab ea glandulis nectariferis crateriformibus majoribus ac quoad numerum plus constantibus (ad foliola proximalia plerumque nullis ad duabus) atque foliolis utroque rhachidis latere plerumque duobus distinguitur.

TYPUS. — Letouzey 14577, Cameroon, Southwest Province, Dikome Balue, 4°55’N, 9°15’E, 35 km NNW Kumba , 1200 m, 24 Mar. 1976 (holo-, P; iso-, K, YA).

Small tree, to 14 m tall. Trunk to 35 cm diam. Young shoots produced in flushes consisting of (1-)2-3 internodes plus young leaves at each branch tip (in adult trees) ( Fig. 7 ). Internodes of young twigs (3-)5.5(-11) cm long, modified as myrmecodomatia, swollen, with thick pith; twigs (3-)4(-5) mm diam. at apex tapering to ca. 2-3 mm diam. at base of internode; enlarged pith extending throughout section of twig produced in a single growth flush; ant-cavities each 2-3 internodes long (in adult trees). Swollen internodes absent in seedlings, present only in plants ≥ 50 cm tall. Prostoma of ant-domatia at apex of terminal internode of each flush of growth, opposite leaf insertion, roughly spherical in shape. Leaves 2 (-3)-jugate ( Fig. 9 ). Leaflets elliptic, falcate, apex acuminate to long-acuminate, smallest ones (proximal pair) (6.5-)16(-28) cm long and (2.7-) 6.5(-11) cm broad, largest leaflets (second pair) (7-)17.5(-30) cm long and (3-)7(-12) cm broad. Nectary glands of intermediate size (smooth gland surface oblong, about 1 × 0.75 mm, not surrounded by a raised ring of tissue), usually 2(0-5) on proximal leaflets ( Fig. 5 ), (0-)1(-2) on other leaflets. Racemes short (axis 3-5 cm long), with> 40-60 flowers, axillary on twigs 4-5 mm diam., also sometimes cauliflorous (on trunk up to 10 cm diam.). Flowers 1.8-3 cm diam.; pedicels 0.3-0.5 cm long; calyx colour unknown, sepals 0.8-1.1 cm long; petals mauve-pink to purple, 0.9-1.3 cm long. Ovule number unknown. Size of mature fruit unknown.

This subspecies is also a myrmecophyte; all trees possess swollen hollow internodes occupied by ants. As mentioned above, L. africana subsp. rumpiensis shares a number of traits with subsp. letouzeyi that distinguish these two from subsp. africana . It is distinguished from subsp. letouzeyi by its usually 2-jugate leaves ( Fig. 9 ), the smaller size of its leaflets and stems, the constancy in nectary number, and its restriction to piedmont and submontane forest (above 500 m and probably more commonly above 800 m).

DISTRIBUTION. — This taxon occurs in the Rumpi Hills ( Figs. 3 , 4 ), where it was studied in 5 field sites. Herbarium specimens from three other sites in the Rumpi Hills (see below) also appear to belong here. Material of myrmecophytic L. africana collected from submontane forest on another hill in the Southwest Province (Letouzey 13632 [K, P, YA], from a 960 m hill 55 km southwest of Mamfe) is tentatively placed in this subspecies.

ECOLOGY. — This myrmecophyte, in contrast to the two preceding subspecies, is restricted to submontane forest (and lowland forest transitional to it: “piedmont” [ THOMAS 1995]). As in the other myrmecophytes, internodes are hollowed and occupied by ants, and each adult tree is occupied by a single ant colony. In contrast to the two preceding subspecies, each of which is principally associated with one (or two) ant species, a diverse array of ant species occupy trees in populations of the subspecies rumpiensis (D. MCKEY and R. SNELLING, unpubl. results). Nature of the interactions with ants has not been studied in this subspecies. This subspecies was termed “ L. africana taxon T2” by CHENUIL & MCKEY (1996).

PARATYPES. — CAMEROON, Southwest Province: Steep hillside, 400-850 m, 5 km W of Esukutang Village, D.W. Thomas et al. 7988 ( MO); forest, 500 m, near Masaka-Batanga , D. W. Thomas & Namata 7746 ( MO); forest, 500 m, near Meta village , Nemba et al. 753 ( MO); colline, 960 m (près côte 897) E of piste Abakpa-Mbiofong, 55km SW Mamfe , Letouzey 13632 ( K, P, YA) .

Figures

Fig. 7. — Examples of variation in the unit of growth within the Leonardoxa africana complex. A, a branch tip of L. africana subsp. rumpiensis (Dikome Balue site) showing two recently matured internodes and leaves produced in a flush of growth; these leaves are bright green (shiny in this photograph) and distinct from the older mature leaf (dark green, not shiny) produced in a previous growth flush; arrow marks the base of this flush. Bar = 10 cm. B, a branch tip of L. africana subsp. africana (Bombe Bakundu site) showing the one-leaf and internode unit of growth typical of all populations of this subspecies. Bar = 2 cm.

Fig. 9. — Typical leaves of the Leonardoxa africana complex, all drawn at same scale. Bar = 10 cm. A, L. africana subsp. gracilicaulis; B, L. africana subsp. rumpiensis; C, L. africana subsp. letouzeyi; D, L. africana subsp. africana.

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. 3. — Geographic distribution of field localities of members of the Leonardoxa africana complex: L. africana subsp. gracilicaulis = Group 1; L. africana subsp. rumpiensis = Group 2; L. africana subsp. letouzeyi = Group 3; L. africana subsp. africana = Group 4.

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.