特徵描述

作者

SHEN, CHUNG-FU and TSOU, CHIH-HUA

型態特徵

Monogeneric (Cycas), evergreen, dioecious, palm-like trees or shrubs; trunk columnar, covered with persistent woody petiole-bases. Leaves pinnately compound, large, spirally arranged, (0.8–) 1–2 (–3) m long, (15–) 20–30 (–40) cm broad, linear to lanceolate, apex acute or obtuse, rarely emarginate, the basal leaflets often reduced to spines; ptyxis of the whole compound leaf involute with the rachis erect and the pinnae circinate, ptyxis of the first compound leaf circinate (in seedling stage); leaflets numerous but rarely over 200 pairs, long linear to very narrowly lanceolate, (10–) 15–30 (–40) cm long, (3.5–) 5–18 (–25) mm broad, entire with margin slightly thickened or somewhat revolute, single-veined, chartaceous to thick-coriaceous, in C. micholitzii generally (sub) dichotomously branching once or even twice, generally somewhat tapering towards base and then attaching to the rachis decurrently with the lower side generally decurrent to a greater extent, without a clearly-defined petiolule. Male cones shortly peduncled, terminally and generally singly borne, narrowly ovato-cylindric or fusiform; male sporophylls numerous, narrowly wedge-shaped with a somewhat projecting, upward-pointing (when long) apical extension and a somewhat clear abaxial ridge, spirally and tightly arranged along an axis, each with numerous pollen-sacs spread over its lower surface. Female sporophylls numerous, mostly very thick, hard, club-like (in C. rumphii complex) or spade-like, densely yellowish/tawny-tomentose at least when immature, spirally borne on the top of the trunk, in most species leaning together to take a broadly ovoid or peach-shaped "cone-like" appearance in both pre- and post- fertilization stages, but in C. rumphii complex generally loosely arranged throughout their presence, comprising a lower fertile stalk and an upper sterile lamina, the former bearing (1–) 2–4 (–5) ovules along each side of its upper portion, the latter either ovate/rounded and pinnatifid or narrowly rhombic and dentate (in C. rumphii complex); ovules erect, with micropyles directing obliquely upward, nearly globose, broadly elliptic, broadly oblong, or broadly obovate, mostly somewhat compressed, ca. 5–13 mm long, glabrous in most species but densely tomentose in the remaining, in C. rumphii complex half-sunken in a notch that is further encircled by a collar. Seeds drupe-like; envelopes 3-layered in most species but 4-layered in C. rumphii complex; the two cotyledons generally united at their base to form a tubular sheath; germinating hypogeally.

屬

The genus Cycas is composed of about 30 species. It is geographically centered in the southeastern part of Asia, with a range enclosing Madagascar and its neighboring part of continental Africa, Comoros, S India, Sri Lanka, SE Himalayas, S China, S Japan, N Marianas, Solomons, Samoas, Tonga, Fiji, New Caledonia, and N and NE Australia. Only one species is native to Taiwan (endemic also).