Lynn G. Clark, J.K. Triplett. Flora of North America 24: 17 - 20
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; auriclesusually 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'.