Monographs Details: Morus
Berg, Cornelius C. 2001. Moreae, Artocarpeae, and (Moraceae): With introductions to the family and and with additions and corrections to Flora Neotropica Monograph 7. Fl. Neotrop. Monogr. 83: 1-346. (Published by NYBG Press)
Description:Genus Description - Trees, dioecious or sometimes monoecious, deciduous; shoot apices shed; axillary buds with bud scales; uncinate hairs lacking. Leaves alternate and distichous; lamina pinnately veined; margin crenate to serrate; stipules free, lateral. Inflorescences unisexual (or bisexual), solitary or paired in the axils of normal leaves or in the axils of scale leaves at the base of lateral (short-) shoots, racemose to spicate to subcapitate, pedunculate, bracteate or ebracteate; flowers ± distant, pedicellate or sessile; tepals free or basally connate, decussate-imbricate; pistillode usually quadrangular; ovary free; stigmas 2, tongue-shaped, equally long. Fruiting perianth enlarged, ± fleshy, reddish (to blackish); fruit (sub)-drupaceous; endocarp crustaceous with a placental woody plug; seed small, with endosperm, the testa with a suborbicular thickened vascularized part below the hilum; embryo curved with equal and flat cotyledons, not enclosing the long radicle.
Discussion:Morus is, remarkably enough, the only small genus of the Moraceae that has not been revised, and, therefore, the number of species, between 10 and 13, is uncertain. The genus is a northern-temperate element with extensions to the tropics, at high elevations in tropical America (M. insignis) and SE Asia (M. macroura Miquel), but in continental Africa as lowland forest species (M mesozygia A. Chevalier).Kunth (1817) created two names in the genus, Morus celtidifolia and M. corylifolia, based on material collected in Ecuador. A third one, M. mexicana, was described by Bentham (1841), based on material from Mexico. Quite different was the material from Colombia used for the description of M. insignis by Bureau. Synomyms to the latter species have been added by Koidzumi (1930), Leroy (1949), and Legame (1973), based on material from Peru, Colombia, and Argentina respectively, whereas Rusby (1911) added one to M. celtidifolia.Leroy (1949) subdivided the genus into three subgenera: Eumorus, Gomphomorus Leroy (1949), and Afromorus A. Chevalier (1949). Subgenus Eumora comprised all species except for the neotropical M. insignis and its synonym M. trianae, which were placed in subg. Gomphomorus, and the African M. lactea (Sim) Mildbraed (= M. mesozygia A. Chevalier), which was placed in subg. Afromorus. Venation patterns of the lamina, abundance, shape and texture of the bracts, and features of the pericarp and embryo were used to distinguish the subgenera. These differences seem to justify infrageneric subdivision, but at most at the section level. However, a comparison of the montane species, M. insignis and M. macroura, showing clear similarities, has to precede further decisions.The association of the genus with the northern-temperate zone is expressed morphologically. At the end of the growing season the apical meristems of the long-shoots abort and are abscised. Beside the "terminal" lateral buds one can find a short stump, which can still be traced to the older wood. From the "terminal" axillary buds the long-shoots elongate in the next growing season. Growth is thus intermittent (accompanied by shedding of leaves) and it is sympodial. The axillary buds are well-developed in Morus celtidifolia, but are small in M. insignis; these buds are provided with bud scales. The leaf venation in M. insignis differs from other Morus species in lacking a clear tendency towards a trinervate or subpalmate pattern, thus being more pronouncedly pinnately veined. The staminate inflorescences are spicate to racemose. The pistillate inflorescences are mostly (sub)capitate heads in the genus, but in M. insignis they are elongate and similar to the staminate ones. In contrast to other Morus species, the bracts are abundant, peltate and subcoriaceous in M. insignis. Morus insignis is associated with humid montane or subtropical conditions, being an element of cloud forest, but M. celtidifolia is a species of drier habitats.Two Morus species have been introduced from Asia: M. alba (rather common) and M. australis Poiret (rare). The latter can be easily confused with M. celtidifolia, but it can be distinguished by the ca. 1 mm long style of the pistillate flower.