Genus Myrianthus in Family Urticaceae

Genus Description

Myrianthus (P.Beauv.) is a small dioecious genus of trees and treelets placed in Moraceae, tribe Doronycheae (Berg et al., 2005). The most frequently treated component of a once broader Myrianthus concept, it is now circumscribed to include species formerly placed in Triovia; those taxa are often cited under Myrianthus in older floras (Whitehouse & Cheek, 2000; Berg et al., 2005; African Plant Database, 2024). Depending on taxonomic concept, the group contains about 6 to 10 species distributed across tropical Africa and the Gulf of Guinea islands (POWO, 2024; WFO, 2024). The type species is Myrianthus arboreus P.Beauv. (Tropicos, 2024).

The genus is diagnostic in Moraceae by its very large, 3–5-lobed to palmately compound leaves with prominent, persistent stipules forming a caducous caducous “prophyll” envelope, and densely tomentose young growth. Plants are medium-sized to emergent trees with milky latex. The inflorescences are unisexual, paired at leafless nodes; female heads are large and fleshy with numerous tiny flowers embedded in a receptacle, forming a fig-like syconium that ripens into a large, indehiscent aggregate fruit often orange to purplish when mature (Berg et al., 2005). Ovary position is inferior, with free styles or short united styles; ovules are anatropous to campylotropous.

Diversity is greatest in West and Central Africa, with several regional endemics; M. capensis is confined to the Cape region of South Africa, M. libericus to the Upper Guinea region, and island taxa include the São Tomé species formerly placed in Triovia (Whitehouse & Cheek, 2000; African Plant Database, 2024). The genus occurs in lowland to submontane tropical forest from near sea level to about 1,500 m altitude, often in secondary and riverine forest, and in some areas forms a characteristic component of canopy or gallery forest (Whitehouse & Cheek, 2000; Berg et al., 2005).

Little is published on the biology; the fig-like heads suggest mutualisms with Agaonidae wasps, and the large, indehiscent aggregates imply dispersal by birds and mammals (Berg et al., 2005). Anecdotal chromosome counts of n=14 have been reported for other Moraceae, but a documented base number for Myrianthus is not securely established (e.g., Datwyler & Weiblen, 2004). Taxonomically, the genus has been narrowed through recent revisions, with the Triovia complex transferred out or subsumed; some authors retain Triovia in synonymy of Myrianthus (Whitehouse & Cheek, 2000), whereas recent phylogenetic treatments place Doronycus and Triovia as separate genera in the same tribe, highlighting still unresolved relationships among lineages of Doronycheae (van der Ham et al., 2011; Datwyler & Weiblen, 2004). Consequently, species limits and sectional classification remain provisional (POWO, 2024; WFO, 2024; African Plant Database, 2024).

Human relevance remains modest: M. arboreeus produces edible fruit and is occasionally cultivated or retained in agroforestry; other species are harvested for timber or grown as ornamental shade trees, but none are major crops (Whitehouse & Cheek, 2000). Conservation concerns include localized habitat loss and uncertain threat status; many taxa lack assessment, and in some regions they occur outside protected areas (African Plant Database, 2024; WFO, 2024). Further field studies and phylogenetic work are needed to clarify species boundaries, confirm chromosome numbers, and update Red List assessments.

• Myrianthus arboreus (P.Beauv.)
• Myrianthus cuneifolius ((Engl.) Engl.)
• Myrianthus fosi (Cheek)
• Myrianthus holstii (Engl.)
• Myrianthus libericus (Rendle)
• Myrianthus preussii (Engl.)
• Myrianthus scandens (Louis ex Hauman)
• Myrianthus serratus ((Trécul) Benth. & Hook.f.)