3. Pennisetum polystachion (Linnaeus) Schultes, Mant. 2: 146. 1824.
牧地狼尾草 mu di lang wei cao
Panicum polystachion Linnaeus, Syst. Nat., ed. 10, 2: 870. 1759; Cenchrus setosus Swartz; Panicum cenchroides Richard; P. erubescens Willdenow; Pennisetum purpurascens Kunth; P. setosum (Swartz) Richard.
Short-lived perennial or annual. Culms much branched, 50–150 cm tall. Leaf blades linear, 10–20 × 0.3–1.5 cm, hispid. Inflorescence linear, 10–25 × 0.8–1 cm, yellow or purplish; axis angular with sharp decurrent wings below the involucres, these densely packed, often speading at right angles at maturity; involucre with numerous bristles obscuring the single spikelet, densely ciliate in lower half with crinkled matted hairs, longest bristle 1–2 cm. Spikelet narrowly lanceolate, 3–4.5 mm; lower glume absent or a small triangular scale; upper glume as long as spikelet, 5-veined, obtuse, ciliolate, apiculate; lower floret staminate or neuter, lemma similar but slightly shorter, obtusely 3-lobed; upper floret 2/3 spikelet length, cartilaginous, smooth, shiny, readily deciduous at maturity; anthers without hairs at tip. 2n = 54.
Naturalized. Hainan, Hong Kong, Taiwan [throughout the tropics].
This is a widespread and polymorphic species, sometimes cultivated for pasture or fodder. The soft, crinkled hairs around the spikelet and the deciduous upper floret are clear-cut characters for recognition.