Cofrin Center for Biodiversity

Botany and Taxonomy

by UWGB graduate student Juniper Sundance

Wild rice is the common name for plants in the genus Zizania. Worldwide, there are 4 species, two of which are native to Wisconsin: Z. aquatica and Z. palustris. Both of our species have two varieties.(Terrell 2007). For many years, however, the different species and varieties in Wisconsin were all considered to be varieties of Z. aquatica. Older literature on wild rice generally mentions only that one species, if any latin name is given, so these sources cannot be used as an indication of the distribution of any single species but of the genus as a whole. A few herbarium vouchers have been examined and annotated with the new taxonomic name, but this has not been done for the majority of Wisconsin vouchers.

Zizania male flower.

Zizania is a member of the grass family ( Poaceae). Z. aquatica and Z. palustris are both annuals, relying on seed germination every year for survival though not all seeds germinate in the same year. The seeds must be submerged in water to germinate. Zizania is monoecious—the female seed-producing flowers develop at the top of the stem, above the male pollen-bearing flowers. Some plants do have a small percent of perfect (having both male and female parts; hermaphroditic) flowers (Liu et al., 1998). Generally the male and female flowers on one plant are not in anthesis (opened, ready for pollinating) at the same time. This enhances cross-pollination and limits inbreeding. Pollen is spread by wind; Zizania is not dependent on specific pollinator interactions. Although bees have been observed gathering pollen, they do not visit the female flowers and so do not contribute to pollination (Terrell and Batra, 1984).

The growth form of Zizania changes as it develops. After germination, submerged young plants have ribbon-like leaves which move easily in the current and, unfortunately, get tangled in (and uprooted by) boat motors, paddles, and oars. As plants grow taller, they show a “floating leaf” stage—the bottom leaf surfaces develop a waxy coating and the upper surfaces are able to exchange oxygen and carbon dioxide in the air. Later, the culm, or seed stalk, with “flag” leaves emerges above the water. The rice plant “tillers”, developing multiple stems in a clump from the same root.

Zizania only grows in a limited range of water depths, within the littoral zone, and is susceptible to water level changes. Water that is too deep prevents sufficient light from reaching the submerged seedlings. Water that is too shallow, preventing good development of floating leaves, leads to a poor crop (Aiken et al. 1988). Flooding during the floating leaf stage can uproot the plant and interferes with oxygen and carbon dioxide exchange through the leaf upper surface. Flooding during the emergent stage could interfere with pollination.

Zizania in water.

Literature Cited

Aiken, SG, PF Lee, D Punter, and JM Stewart. 1988. Wild rice in Canada. Agriculture Canada Publication #1830. Toronto.
Liu, Q., EA Oelke, RA Porter, and R Reuter. 1998. Formation of panicles and hermaphrodite florets in wild-rice. Int’l Jl Plant Sci 159:550-558.
Terrell, EE. 2007 . Zizania L. in Flora of North America. Vol 24: Magnoliophyta: Commelinidae (in part): Poaceae, part 1. Barkworth, ME, Capels, KM, Long, S, Anderton, LK, and MB Piep. Oxford University Press: NY. pp 47-51.
Terrell, EE and SWT Batra. 1984. Insects collect pollen of eastern wildrice, Zizania aquatica (Poaceae). Castanea 49(1): 31-34.

Biodiversity Topics: Introduction . Plants . Animals . Mammals . Birds . Reptiles & Amphibians . Arthropods . Spiders . Insects