Sparganium erectum L.

Family: Sparganiaceae

Common names:  exotic bur-reed, branched bur-reed, simplestem bur-reed

Disseminule:  Fruit

Description

Fruit an achene, 4.5-7.5 mm long (not including beak), 1.5-4 mm wide and thick. Obpyramidal, but angles sometimes softened due to crowding, usually with a distinct shoulder between upper and lower parts, elliptic or oblong to obtrullate in outline, round to angled in cross section. Lower part pyramidal to narrowly obconical, sometimes ridged, usually with 3-4 persistent tepals attached at base and ending at shoulder (+/- appressed) to edges. Upper part dome-shaped, persistent style base forming a beak. Indurate; surface +/- wrinkled, lustrous, light brown to brown, often grading to darker brown at apex. Endocarp stony, ridged. Embryo axile-linear; endosperm present.

Identification remarks

The ridges on the lower portion of the achene are more conspicuous on shriveled fruits. Sparganium erectum can be distinguished from other species in the genus Sparganium by its shape in two distinct sections. Compare with Sparganium eurycarpum Engelm.

Distribution

Southwestern temperate Asia, Europe, Morocco, Australia.

Habitat

Muddy or shallow water at margins of ponds, lakes, streams; in ditches and swamps.

General information

Sparganium erectum is an emersed aquatic herb, to 1.5 m tall. A widespread aquatic plant, it can form dense colonies, hindering waterflow. Some authors have considered S. erectum L. to include the Eurasian population, as well as the North American population, called S. eurycarpum Engelm. Here, S. erectum is considered just the Eurasian population.

Fruits

Fruits

Fruits

Fruits with spongy layer mostly removed, exposing stony, ridged endocarp

A, Fruit; B, fruit with spongy exterior removed; C, longitudinal section of fruit showing embryo; D, transection of fruit

drawing by Lynda E. Chandler

Fruits