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Prairie Grasses

Past and Potential for Ontario's Natural Heritage - Page 3

Botanical and biological attributes of tallgrass Poaceae - The family Poaceae is a group of flowering vascular plants (Class Angiospermae) which are monocots (Subclass Monocotyledoneae) and members of Superorder Commelinanae, Order Poales. Zomlefer (1994) characterizes the family as one of

Tufted, herbaceous plants with rhizomes or stolons; terete stems with hollow internodes and jointed nodes; 2-ranked linear leaves with a ligule and an open basal sheath; spikelets arranged in various inflorescences; anemophilous, inconspicuous flowers subtended by 2 bracts (palea and lemma); reduced perianth of scales (lodicules); deeply sagittate, functionally versatile anthers; 2 feathery stigmas; and a caryopsis as the fruit type. Silica present (deposited throughout the plant). Anatomical features: several distinctive modifications of the leaf (including ligules and auricles).

This large plant family has been further divided into two to twelve sub-families and up to sixty tribes (Zomlefer 1994), but recent treatments (e.g., Gould and Shaw 1983) accept five or six sub-families based on various morphological differences (Zomlefer 1994). Appendix 1 lists 30 Poaceae species native to Ontario and associated with tallgrass communities in southern Ontario. Each of these belong to one of three sub-families: Pooideae, Panicoideae, and Chloridoideae (Zomlefer 1994; Voss 1972).

Most tallgrass Poaceae require full sun, although some savanna species may grow in the light, partial shade of open grown oaks or pines (e.g. Panicum dichotomum, Stipa avenacea; Dore and McNeill 1980). Many are bunch grasses (as opposed to turf grasses) and they have deep fibrous root systems, most extending five to seven feet (Kline 1997). Tallgrass species thrive in a nitrogen-poor environment (Wedin and Tilman 1992). Many of the grass species photosynthesize via the C4 pathway (Kline 1997). This is a logical adaptation, since C4 plants are more efficient than C3 plants in hot dry conditions (Moore et al. 1995) often associated with tallgrass communities. In practical terms, it means that most prairie grasses lie dormant until later in the spring, but are still green and actively growing through the late summer, when cool season grasses have browned and become dormant. Tallgrass prairies are considered among the most productive vegetation types in the world (Kline 1997).

Most members of the grass family are anemophilous, and seed dispersal mechanisms include wind and animal transport (Chapman 1996). Fruit of various Ontario tallgrass Poaceae species bear awns, while various tallgrass forb species bear hairs, hooks or burrs, which are adaptations for epizoochorous animal dispersal. An impressive example is Stipa spartea, aptly called porcupine grass or needle grass, which may bear awns up to 20 cm long (Dore and McNeill 1980).

The average grass to forb ratio in Ontario tallgrass communities is estimated to be 50:50, with the grasses helping to provide structure and support to the diversity of forb species (A. Woodliffe, pers. comm.).

Elymus canadensis

Elymus canadensis (Canada wild-rye).
Panicum virgatum

Panicum virgatum (switchgrass).
Sporobolus elongatus - photo: N. G. Dengler Sporobolus elongatus leaf in transverse section; note the conspicuous bundle sheath cells (BSC) of this C4 grass in which C4 acids formed in the mesophyll carboxylate ribulose bisphosphate to form the C3 acids used in sugar and starch synthesis. Photo: N. G. Dengler 1998 Botany Department, University of Toronto.

Page 1 2 3 4 5 6 7 8 9 10 References Appendix 1

| What are plant families? | How do we distinguish them? | How and why do we study them? | Selected vascular plant families of Ontario | Reading List | Course outline |

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Page design © 1999 T. A. Dickinson; essay text and illustrations © 1998 Lindsay Rodger except as noted.
Please send your comments to tim.dickinson@utoronto.ca; last updated 7-May-99

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