4. Morus L. (mulberry)
Plants trees to
20 m tall (shrubs elsewhere), unarmed, with milky sap. Bark shallowly grooved
longitudinally, light to dark brown, sometimes yellowish-, orangish-, or
reddish-tinged. Twigs slender to stout, not or only slightly zigzag, reddish
brown to greenish brown, usually with circular to elongate, light or dark brown
lenticels, minutely hairy or nearly glabrous, the winter buds 3–7 mm long,
ovoid, bluntly to sharply pointed at the tip, with several overlapping scales,
glabrous or hairy, especially along the margins, sometimes shiny. Leaves
alternate, the petiole 2–5 cm long, minutely hairy or nearly glabrous. Leaf
blades ovate, unlobed or shallowly to deeply (2)3–5-lobed and with 3 or 5 main
veins from the base, the margins otherwise toothed, the upper surface bright
green, roughened or smooth and glabrous to sparsely hairy, the undersurface
lighter green, sparsely to densely pubescent with short, nonwoolly hairs.
Inflorescences entirely staminate or pistillate, dense catkins, the calyces,
deeply 4-lobed (occasionally 5-lobed in M. alba), 1–2 mm long, the lobes
ovate to broadly elliptic-ovate and somewhat concave, hairy, often
reddish-tinged. Staminate inflorescences solitary in the leaf axils. Pistillate
inflorescences solitary in the leaf axils (but sometimes appearing clustered on
short shoots), the style 2-branched, the stigmas linear. Fruits consisting of
crowded, ovoid to short-cylindric clusters of ovoid achenes, these covered by
the fleshy, white, red, purple, or black calyces, each aggregate shed as a
unit. About 10 species, North America, Europe, Asia.
The mulberry
fruit superficially resembles a blackberry, but its structure is totally
different. The mulberry consists of tightly clustered fruits of many adjacent
flowers, and the fruitlets are not true drupes; the juicy part develops from
the calyx and the true fruit is an achene, the dry, so-called stone inside it.
In contrast, a blackberry consists of numerous ripened ovaries on an expanded
receptacle within a single flower and the individual fruitlets are true drupes.
Mulberries are
hardy, fast-growing small trees that produce sweet fruit in very high yield
from a young age. The fruit is attractive to many species of birds and mammals.
Both of our species are eaten by humans, but they are considered much inferior
in flavor to those of the black mulberry (Morus nigra L.), an Old World
species. Mulberries can become aggressive and weedy in gardens.
Quickly growing
saplings or root sprouts sometimes produce relatively large leaves that are
deeply and irregularly palmately 5-lobed, with the relatively slender lobes
bluntly and irregularly lobed, scalloped, and/or bluntly toothed. These
sometimes are mistaken by gardeners for ornamental figs (but Ficus L.
species generally are not winter-hardy in Missouri) or young maples (but Acer
species have opposite leaves). Lobed leaves are seen relatively commonly in M.
alba, but are far less frequently encounted in M. rubra.