eastern gamagrass (gamagrass, bullgrass, sesame grass)
Tripsacum dactyloides (L.) L.

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planthabithabitinflorescenceinflorescencespikeletsspikeletsillustration

Eastern gamagrass is a close cousin of maize that is widely distributed in the eastern and central United States to northern South America. In Iowa, eastern gamagrass is relatively uncommon and restricted to the southern half of the state, where it grows on low moist ground, in prairies, or even along roadsides, especially in ditches. It is unique among Iowa grasses in having separate male and female spikelets with the female spikelets sunken into the hardened, thick joints of the lower part of the flowering heads. It is also one of the taller and more robust grasses found in Iowa, rivaled only by maize (Zea mays subsp. mays), common reed (Phragmites australis), and silver plume grass (Miscanthus sacchariflorus). Eastern gamagrass flowers from July through October—the orange-yellow anthers are quite beautiful. Overall, this species is very striking and has potential as an ornamental.

Etymology: According to the FNA treatment of this genus, the origin of the name Tripsacum is obscure; dactyloides is from the Greek dactylus = finger and –oides = like or resembling, referring to the arrangement of the branches of the flowering head like the fingers of a hand.

 

Plants perennial, in large clumps, with short knotty rhizomes. Culms 1-2.5 m tall. Leaves with sheaths smooth; ligules a short fringed membrane; blades 30-52 cm long, (5-) 14-19 mm wide, flat, the midrib fairly prominent and whitish at least on the upper surface. Flowering heads terminal and axillary, 12-22 cm long, with 1-3 branches from the base, each branch bearing several female spikelets below and many pairs of male spikelets above. Female spikelets 6.5-7.5 (-9) mm long, solitary, each sunken into a hardened, thick joint of the main axis, these breaking apart when ripe; lower glume ovate, hardened, tapering at the tip, concealing the rest of the spikelet. Male spikelets paired, both lacking stalks or one with a very short stalk, (5.5-) 7-10 mm long; glumes slightly leathery to papery, as long as the spikelet and completely enclosing the two male florets; lower glumes two-keeled, slightly leathery, acute or notched at the tip. Chromosome number 2n = 36, 54, 72.

 

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