Pentaclethra Benth., J. Bot. (Hooker) 2: 127. 1840.
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https://dx.doi.org/10.3897/phytokeys.240.101716 |
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https://treatment.plazi.org/id/4FD8E9CA-94FB-429C-B9BF-C10D717D1CD1 |
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scientific name |
Pentaclethra Benth., J. Bot. (Hooker) 2: 127. 1840. |
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Pentaclethra Benth., J. Bot. (Hooker) 2: 127. 1840. View in CoL
Figs 104 View Figure 104 , 105 View Figure 105 , 106 View Figure 106 , 107 View Figure 107
Type.
Pentaclethra filamentosa Benth. [≡ Pentaclethra macroloba (Willd.) Kuntze (≡ Acacia macroloba Willd.)]
Description.
Large, unarmed, often buttressed trees 10-35 m tall, (Fig. 104C View Figure 104 ) to 1.3 m in diameter, adventitious roots sometimes present; bark mottled grey/brown, smooth; young stems with dark brown stripes when dried, pubescent with rusty or golden appressed hairs, brachyblasts absent. Stipules small, linear, caducous. Leaves large, bipinnate, foliar nectaries absent; pinnae 5-20 pairs per leaf, opposite, petiole and pinnae adaxially pubescent with erect golden or rusty hairs; leaflets 10-60 pairs per pinna, opposite, sessile, oblong to linear-falcate, glabrous. Inflorescence a terminal panicle of spikes (rarely solitary) (Fig. 105G View Figure 105 ), axis bearing hundreds of tiny sessile flowers, the spike 5-20 (30) cm long, to 3.5 cm broad at anthesis. Flowers 5-merous; sepals connate, calyx campanulate, lobed, glabrous, green to yellow, calyx lobes imbricate in bud; petals connate, valvate in bud, glabrous, fleshy, the margins of the lobes inrolled and the apex of each petal keeled, white, green, or pink to red in colour; androecium fused to the petals forming a stemonozone, filaments sometimes connate above the petals as well, each flower with 5 fertile stamens alternating with 5 sterile staminodia, the latter opposite the petals, filamentous, white to cream, exserted beyond the corolla, fertile stamens with the filaments white, anthers dorsifixed, oval, opening by pouches, each bearing a large anther gland at the apex; pollen of tricolporate monads; ovary sessile, rusty-pubescent, linear to ovate, style equal to or shorter than the fertile stamens, stigma punctate. Fruit a woody, explosively dehiscent legume, valves curling after dehiscence, 15-50 (65) cm long, oblong, clavate, 5-8-seeded; exocarp dark brown, glabrous, striate with longitudinal veins; endocarp smooth, light brown, fibrous, not partitioned between the seeds. Seeds large, recalcitrant, inserted obliquely, orbicular to ovate, 4-7 × 2.5-3.5 cm, testa papery, pleurogram absent (Fig. 106F View Figure 106 ).
Chromosome number.
2 n = 26 ( Fedorov 1969; Goldblatt and Johnson 1990).
Included species and geographic distribution.
Three species, one in Latin America, widespread from Central America (Guatemala, Costa Rica, and Panama) into South America (Venezuela, Colombia, and Brazil), and the islands of Trinidad and Tobago; two species in West Africa, from Senegal to Angola and the Congo, also the islands of Principe and San José (Fig. 107 View Figure 107 ).
Ecology.
Lowland humid and sub-humid forests, often on riverine or waterlogged soils, sometimes the dominant tree species particularly in the Americas. Seeds are demonstrated to be hydrochorous in Pentaclethra macroloba ( Williamson and Costa 2000).
Etymology.
Claimed to be from the Greek, pente (= five) and kleithro (= bolt), alluding to five imbricate sepals and five petals joined at their bases ( Barroso et al. 1991).
Human uses.
Pentaclethra macrophylla has many traditional uses, and is often planted around homes to shade gardens, improve soil fertility, and provide food, medicine, and timber. Known as the African oil bean tree, Owala oil tree, or Atta bean, the seeds are either roasted for up to 12 hours or fermented for several days to make an edible paste called ugba, high in protein and oil ( Achinewhu 1982). Oil from the seeds also has antimicrobial properties and is a promising natural ointment for wounds ( Ugbogu and Akukwe 2009). Leaves and bark are used medicinally as an anti-diarrheal, the scientific basis of which has been demonstrated ( Akah et al. 1999). Although nitrogen fixation was not confirmed scientifically until 1993 ( Ladipo et al. 1993), the trees have long been grown in Nigeria as a green manure crop. Pentaclethra macroloba has many of the same traditional uses as the African species, as a source of wood, medicinals, and oil. The oil from this tree is known as "Pracaxi oil" or "Pracachy oil" and is high in behenic acid, a compound important to the cosmetic industry for its moisturizing properties. It is being commercially marketed as a natural botanical for skin problems.
Notes.
Pentaclethra is often considered a transitional genus between the core mimosoids and the rest of the Caesalpinioideae . It shares a number of characters with the genus Dimorphandra Schott such as woody, clavate pods, flowers bearing staminodia alternating with fertile stamens, and imbricate sepals; however recent studies have shown the floral characters to be independently derived ( Barros et al. 2017).
The genus has been considered a classic example of a Gondwanan distribution, being disjunct between western Africa and Central and South America. The very short-lived (recalcitrant) seeds with a thin, papery testa coupled with a heavy, elastically dehiscent fruit seems to preclude a dispersal event across the Atlantic, although the much younger age now estimated for the legume family argues against a vicariant distribution. It is intriguing that P. macrophylla occurs on islands off the west coast of Africa and P. macroloba in Trinidad and Tobago. Seeds of P. macroloba are hydrochorous in freshwater ( Williamson and Costa 2000; Rocha-Dantas et al. 2021) and two of the species are quite common on coastal plateaus. It would be interesting to test if the seeds remain viable in salt water, thus providing a means of amphi-Atlantic dispersal.
Taxonomic references.
Flores (2002); Schery (1950), illustration; Villiers (1989), illustration.
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