Arundo donax L., giant reed, Spanish cane. Perennial, bamboolike, evergreen with overwintering leaves on principal canopy shoots, clonal, rhizomatous, fibrous–rooted, aboveground principal shoots erect to ascending, with 1—several ascending to spreading lateral branches from any node midplant (or at any node when plant damaged), in range 250—800 cm tall; shoots with only cauline leaves, essentially glabrous; rhizomes shallow, horizontal and long–creeping, typically 30—60 mm diameter (mature plants), with brownish scales; adventitious roots on lower side of rhizome
Stems (culms) cylindric, of principal axes (1° shoots) living 2 or 3 years, (16—)24—33+ mm basal diameter and becoming woodlike before year 2, of lateral shoots pencil–like and rigid, < 14 mm diameter, internodes 50—290 mm long; internodes hollow.
Leaves alternate distichous, simple with sheath, on each lateral shoots dimorphic with a distinctive first leaf (prophyll); prophyll with overlapping open sheath, triangular–deltate in outline and strongly 2–keeled and stiff–biconvex, 6.5—9 mm long, green with narrow membranous margins, keels + adjacent surfaces densely sericeous, the hairs 4—5 mm long, silvery white; sheath open, not keeled, persistent and gray or brownish after blade abscises, collar yellowish tan, wavy and rounded on margin, long–villous at basal margin; ligule membranous and ciliate, 1—1.6 mm long, as wide as leaf blade; blade narrowly lanceolate, gradually long–tapered (small and triangular for 1—2 blades next to rhizome), (35—)120—860 × 15—77 mm, < and narrower on lateral shoots, dull, somewhat glaucous, flat, minutely toothed on margins, with long, linear tip, parallel–veined with midvein conspicuous on basal 1/3.
Inflorescence spikelets, in terminal panicles, panicle plumose, 380—550 × 80—150 mm, with alternate distichous clusters of ascending lateral branchlets, branchlets stiff, 50—220(—270) mm long, typically with grayish and purplish spikelets, spikelet with 3—5(—6) florets, bracteate, short–awned; branch and branchlet axes low–ridged, minutely scabrous, the stalk beneath a spikelet minutely short–hairy.
Spikelet slightly compressed side–to–side, in range 11—13 mm long (including awns), bisexual (the terminal floret sterile and diminutive), breaking above glumes and between florets; glumes 2, ± equal, lanceolate and long–acuminate, 8.5—11.5 mm long, ± without awns, membranous and often purplish on rounded back, with 3 or 5 veins, the veins raised especially on upper glume with midvein only extending to tip, glabrous; rachilla flattened, ± 0.5 mm long and pubescent between glumes, ± 0.2 mm long below first floret with basal tuft of hairs, segments 0.8—2 mm long and glabrous, forming the longest internode below the terminal (sterile) floret; lemma awned, lanceolate, 10—12 mm long (including awn), tannish scarious, rounded on back, 2–forked having teeth or bristles with awn arising from notch, teeth sometimes with bristle tip, 5—7–veined basally to 3–veined at tip for teeth and awn, conspicuously pilose below midpoint, the hairs fine, 4.5—8 mm long, veins green becoming purplish approaching tip, the awn 2—2.8 mm long, delicate, bristle tips 1—2 mm long; palea < lemma, oblanceolate, 3.5—5.5 mm long, mostly colorless but pale green at base and sometimes purplish at tip, truncate or slight notched and conspicuously short–ciliate at tip, 2–veined, 2–keeled, densely and fine–hairy along keels, sparsely pilose at base.
Flower bisexual; perianth (lodicules) 2, ± inversely pyramidal to trapezoidal or ± 3–toothed with short, rounded to obtuse lateral teeth and an elongated middle tooth, 0.3—1.25 × 0.3—0.6 mm, the middle tooth = length of lodicule body, long–tapered at base, hairy or finely fringed and sometimes reduced to a threadlike extension; stamens 3, free; filaments threadlike, 2.5—5 mm long, translucent; anthers dorsifixed (attached to base of connective), dithecal, linear, 1.7—3.2 mm long, yellow–green, connective 0.5—1 mm long, longitudinally dehiscent; pollen pale yellow; pistil 1; ovary superior, ellipsoid, 0.5—0.8 mm long, at anthesis olive green to dark brown, glabrous, 1–chambered with 1 ovule; styles 2, spreading, 2.5—3.4 mm long, dark brown at thickened base and translucent–white below stigmas, stigmatic above midpoint; stigmas exserted sideways from lemma and palea, ± 0.6 mm wide with dense, spreading, purplish to brown hairs.
Fruit achene (caryopsis), oblong, 3—4 mm long, with 2 teeth from persistent style bases.
A. C. Gibson & B. A. Prigge