Shrubs or trees to 10 m, dioecious or monoecious. Bark greyish-white, fissured, scaly. Branches glabrous or sparsely pubescent with circular to elliptic lenticels. Branchlets grey to dark brown, pubescent at first; internodes long relative to M. microphylla. Winter buds conical to ovoid, large, to 1.2 cm. Stipules lanceolate, c. 1 cm, pubescent. Leaves lanceolate to oblong elliptic, rarely lobed, 4–25 × 1–8 cm; upper surface sub-glabrous with a few, distant short hairs; lower surface pubescent along veins, veins often yellowish; base truncate to cordate; margins regularly serrate; apex acuminate to sub-caudate. Male inflorescences 2 per node, 2.5–3 cm, peduncle 0.2–2.5 cm; male flowers distantly set, with green to reddish, rounded to ovoid calyx lobes, filaments filiform. Female inflorescences 1 per node, 1–4.5 cm, on a peduncle 0.5–2 cm, pubescent; female flowers with ovoid calyx lobes, ovary dark green, ovoid, 1.5–2 × 1 mm, glabrous, style absent or very short, stigmas 2, branched, papillate. Syncarps maturing red, dark red or reddish-brown, sometimes appearing dry, short-cylindric, 1–4 cm. (Razdan & Dennis Thomas 2021; Berg, C.C. in Davidse et al. 2015).
Distribution Bolivia Colombia Costa Rica Ecuador El Salvador Guatemala Honduras Mexico Peru
Several authors interpret Morus celtidifolia Kunth quite broadly, sinking M. microphylla Buckley into it; others treat them as separate species, including Flora of North America and Plants of the World Online (Plants of the World Online 2022) whose taxonomy is followed here. In this sense, M. celtidifolia is found in Central America, from Mexico to Panama. Growing wild in the forests of this region when Spanish conquistadors arrived in the early 16th century, M. celtidifolia was used to feed imported Bombyx mori silkworms in small-scale trials by the leader of the invasion, Hernán Cortés, before the better-suited M. alba was introduced and cultivated as a colonial extension of the Spanish silk industry (Marsh 2020). M. celtidifolia was one of a number of species that served as host for the larvae of indigenous moths such as Eucheira socialis, the Madrone butterfly, whose large, communal nests the Aztecs cut and pasted together to make a paper-like fabric (Hogue 1993).
It is hard to determine the extent to which M. celtidifolia is cultivated within our study area; ‘barely if at all’ does not seem an inappropriate assessment. Those few works that refer to it are almost all referring to the Texas Mulberry, treated here as M. microphylla, but even this species can only be said to have a tenuous presence on the very fringes of the temperate zone. BGCI’s Plant Search returns only six ex-situ sites reporting M. celtidifolia in its collections, and it is telling that the Tree Register of Britain and Ireland does not report any notable plants of either M. celtidifolia or M. microphylla from these islands (Tree Register 2022).