Morus alba

White mulberry is a species that was introduced (from Asia) in the 1600’s in an attempt to established a silkworm industry in North America; it has since escaped cultivation. Individual trees are usually either male (with staminate florets in drooping, whitish to yellow-green catkins 1-1.5″ long) or female (with pistillate florets in less obvious green, erect, cylindrical catkins 1.3-3/4″ long), but trees that produce both male and female florets are known. Male florets are 1/4″ long with a tiny green or yellowish four-lobed calyx, four stamens, and no pistil or petals. (BTW, the pollen is released by mechanically flinging it into the air via the catapult-like stamens. See Taylor et al. 2006. Sex. Plant. Reprod. 19: 19–24.) Female florets are 1/4″ long with a tiny green four-lobed calyx, a single, flattened-oval ovary with two diverging white or reddish styles and no stamens or petals. The fruit is a blackberry-like compound drupe that typically changes color from green to white, but some trees have fruit that continues maturation to red and finally to black. (Those producing black fruit are often referred to as var. tartarica, but that name is invalid.) White mulberry can be usually be distinguished from black mulberry by the leaves; the underside of white mulberry leaves is invariably hairless and the top surface smooth, but the underside of red mulberry leaves is covered with small hairs and the upper surface is rough. However, white and red mulberry can hybridize, which can confuse matters significantly.

White mulberry is easily confused with red mulberry (Morus rubra) — both can bear reddish or black fruit — but they can be distinguished by their leaves. White mulberry forms substantial trees 30-60 feet tall common in Jackson Park; the saplings are ubiquitous, probably because the mulberries are so widely consumed by birds. The trunk is short with greyish-brown bark; the bark has shallow vertical furrows and flattened ridges. The leaves are alternate, 2-6″ long and 1.5-3.5″ across, oval in outline. The leaves can be confusing because they can either be (1) a simple oval with a pointed tip or (2) a highly (3-7) lobed leaf with either shallow or deep lobes; the lobes are typically rounded rather than pointed except for the terminal lobe, which is always pointed). In either case, they may have saw-toothed margins or margins with rounded, symmetrical teeth (crenate). White mulberry can be usually be distinguished from black mulberry by the leaves; the underside of white mulberry leaves is invariably hairless and the top surface smooth, but the underside of red mulberry leaves is covered with small hairs and the upper surface is rough. However, white and red mulberry can hybridize, which can confuse matters significantly.