Plants arborescent or subarborescent, spreading or loosely clumped; rhizomes leptomorphic. Culms 0.5-8 m tall, to 3 cm thick, erect; nodes not swollen; supranodal ridges not prominent; internodes terete to slightly flattened or shallowly sulcate above the branches. Culm leaves: sheaths persistent or deciduous, mostly glabrous, abaxial surfaces sparsely pilose towards the margins and apices, margins ciliate; auricles usually present; blades erect or becoming reflexed, narrowly triangular to strap-shaped, abaxial surfaces sparsely pilose; leaves at tips of new shoots crowded into distinctive fan-shaped clusters or topknots, blades expanded as on the foliage leaves. Branch complements of 1 primary branch and 0-2 subequal secondary branches on young culms, rebranching to produce to 40+ secondary branches on older culms. Foliage leaves: sheaths persistent on the lower branch nodes; auricles usually present; fimbriae to 10 mm; blades finely cross veined abaxially, acuminate, blades of the ultimate branchlets often smaller, crowded into flabellate clusters of 3-7 leaves. Inflorescences open racemes or panicles; disarticulation below and between the florets. Spikelets 3-7 cm, with 6-12 florets, basal floret occasionally sterile, laterally compressed. Glumes 1-2, shorter than the lowest lemmas; lemmas to 2 cm, sometimes awned, awns about 4 mm; anthers 3; styles 3; paleas 2-keeled, not exceeding the lemmas. x = 12. Name from the Latin arundo, 'reed'.
Spikelets many-fld, elongate, the rachilla disarticulating between the lemmas; glumes unequal, distant, shorter than the lemmas, these lanceolate, 11-17- veined, about equaling the 2-keeled paleas; lodicules 3, relatively well developed; stamens 3; stigmas 3; woody perennials with slender, hollow culms, freely branched after the first year; lvs linear or lanceolate, with evident cross-veins, tapering to a petiole and articulated with the sheath; spikelets large, in loose racemes or panicles. 150 (depending on generic circumscription), warm reg.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.