Yam

Yam

　　Yam

　　The root is thick, straight-growing, and can reach up to 1 meter in length. The leaves are alternate, becoming opposite from the middle upwards, and rarely whorled in threes. Bulbils (also called "zero-yu-zi") often grow in the leaf axils. The leaf shape is highly variable, ranging from triangular-ovate to broadly triangular-ovate, often with three shallow to deep lobes. The flowers are unisexual, extremely small, and greenish-white, all arranged in spikes. The male inflorescence is erect, the female inflorescence is pendant. The capsule has three wings. It is a perennial twining herbaceous plant; it has a blocky or root-like underground stem; the leaves are alternate, rarely opposite, simple or palmately compound, entire or 0; the flowers are unisexual; rarely monoecious, forming spikes, racemes, or panicles; the perianth has six segments in two whorls, basally fused; there are six stamens, sometimes with three developed and three reduced; the female flowers are similar to the male ones, except the stamens are reduced or absent; the ovary is inferior, with eight chambers, three separate styles; the fruit is a capsule or berry; the seeds have wings.

　　Growth Habits

　　Prefers light and is not cold-resistant. Best grown in well-drained, loose, fertile loamy soil. Avoid waterlogging. The underground yam stem is cylindrical but may become deformed due to varying geological conditions during growth. It is fleshy and thick.

　　First Type of Yam: The stem is cylindrical, the leaves are triangular-ovate to broadly triangular-ovate, with a hastate cordate base. The male inflorescence is a spike, not pendulous, with a mostly zigzagging long axis. The male flowers are nearly sessile, the bracts are triangular-ovate, shorter than the perianth, the perianth segments are six and ovate, the stamens are six and developed; the female inflorescence is similar to the male one, the ovary stigma is three-lobed. The capsule has three wings, the wing length is almost equal to the width, with short stalks, and each chamber contains two seeds located centrally; the seeds are ovoid, surrounded by chestnut-shell-colored thin wings about 6 mm wide, with unequal widths around. Flowering period is June to August, fruiting period is August to October.　

　　Second Type of Yam: Reproduces asexually, the stem is cylindrical, the leaves are heart-shaped, and it produces no flowers. “Yam beans” grow in the leaf axils. After the stems and leaves wither in autumn and winter, the “yam beans” fall to the ground and sprout the following spring.