Leonardoxa africana subsp. letouzeyi McKey, 2000

Mckey, Doyle B., 2000, Leonardoxa africana (Leguminosae: Caesalpinioideae): a complex of mostly allopatric subspecies, Adansonia (3) 22 (1), pp. 71-109 : 100-101

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

Haec subspecies Leonardoxae africanae subsp. africanae arcte affinis, sed ab ea medullae loculo per internodia duo triave continuo, foliorum expansione simultanea ramunculi ad nodos terminales duos tresve, glandulis nectariferis crateriformibus minoribus ac quoad numerum plus variabilibus (ad foliola proximalia plerumque nullis ad duabus) atque foliolis usque ad 30 cm longis utroque rhachidis latere saepe quattuor distinguitur.

TYPUS. — D.W. Thomas et al. 7480, Cameroon, Southwest Province, roadside forest S of Baro Village , 5º14’N, 9º15’E, 250 m, 31 Mar. 1988 (holo-, MO; iso-, WAG).

Small tree, (rarely) to 14 m tall. Trunk to 30 cm diam. Young shoots produced in flushes consisting of (1-)2-3 internodes plus young leaves at each branch tip (in adult trees). Internodes of young twigs (2.8-)7(-13) cm long, modified as myrmecodomatia, swollen, with thick pith; twigs (4-)5.5(-6.1) mm diam. at apex tapering to ca. 2.5-4 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 ≥ 60 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-)4(-5)-jugate. Leaflets elliptic, falcate, apex long-acuminate, proximal ones (13.2-)17(-22) cm long and (4.5-)6(-8) cm broad, largest leaflets (next-to-distal pair) (14.5-) 21(-32) cm long and (5-)7.5(-12) cm broad. Nectary glands absent from some individuals; when present, appearing intermediate in size (smooth gland surface oblong, about 1 × 0.75 mm, not surrounded by a raised ring of tissue) and few in number, usually 0-2 (very rarely up to 5) on proximal leaflets and usually absent on other leaflets. Racemes short (axis 3-5 cm long), with 40-60 flowers, axillary on twigs of up to 1 cm diam., also sometimes cauliflorous. Flowers 1.8-3 cm diam.; pedicels 0.3-0.5 cm long; calyx pale lilac, sepals 0.8-1.1 cm long; petals usually violet, sometimes pink, 0.9-1.3 cm long. Ovules 4-5. Fruit to 15 cm long, 5 cm broad.

The most distinctive trait of L. africana subsp. letouzeyi is the large size of its stems and leaves ( Fig. 9C ). Young twigs are much more robust than those of corresponding age of plants of any of the other subspecies, leaflets are larger, and 4- jugate leaves predominate on most adult trees, in contrast to the 2-or 3-jugate leaves which characterise the other subspecies. Another trait distinguishing the subspecies letouzeyi from all other subspecies is the great variation among individual trees of the same population in the number of foliar nectaries. This subspecies shares with subsp. rumpiensis several traits that together distinguish them from subsp. africana : (1) Antcavities are first produced in juveniles over 50 cm tall; (2) ant-cavities in adult trees extend over 2-3 internodes, corresponding to the units of growth produced in flushes; (3) vegetative growth is synchronised over the crown of the tree; (4) the prostoma is roughly spherical in shape ( Fig. 6C ).

DISTRIBUTION. — This subspecies occurs in the wettest forests of Africa, the lowland forests near the Bight of Biafra ( Figs. 3 , 4 ). It is found from Uwet Division, Calabar Province, Nigeria, through Korup National Park on Cameroon’s border with Nigeria, and throughout the Mamfe Plain and Cross River area. Its range extends northward at least to the Takamanda Forest Reserve north of Mamfe. The eastern limit of its distribution is uncertain.

ECOLOGY. — This subspecies is a myrmecophyte in which swollen stems may first appear in juveniles about 60 cm tall (but more commonly in saplings 1 m or taller). While saplings are associated with small colonies of any of several species of twig-nesting ants, mature individuals are occupied solely by the formicine ant Aphomomyrmex afer , which protects young leaves of the host tree against insect herbivores ( GAUME 1998; GAUME & MCKEY 1998). This subspecies was termed “ L. letouzeyi ” by MCKEY (1991) and “ L. africana taxon T3” by C HENUIL & M C K EY (1996), GAUME et al. (1998) and GAUME & MCKEY (1998). The ant occupants of this subspecies tend scale insects and mealybugs inside the hollow stems of the host ( GAUME et al. 1998), in contrast to the ants associated with the subspecies africana , which never tend homopterans. (For the subspecies rumpiensis, more information is required on this point.) As argued by GAUME et al. (1998), this dependence on homopterans is related to the low and variable number of foliar nectaries in this subspecies.

PARATYPES. — NIGERIA, Uwet Division: Calabar River , Latilo 35 ( BR, K, P) ; Oban, Talbot 1440 ( K) . — CAMEROON, Southwest Province: Bamenda Road, Mile 43 from Mamfe , 1,500 ft (460 m), Coombe 191 ( BR, K) ; Akpasang River , Korup National Park, McKey 72 ( P, YA) ; Korup National Park, between Mana River bridge and Camp 1, Manning 1714 ( MO) ; disturbed forest near Ndian Oil Palm Plantation , 50 m, D.W. Thomas 4269 ( BR, US) ; Takamanda Forest Reserve, near Matene , 170 m, D.W. Thomas 4527 ( MO) .

Figures

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. 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. 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.