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Growth Patterns of Some Native Annual and Perennial Herbs in Southern Wisconsin

Struik, Gwendolyn J.
Ecology 1965 v.46 no.4 pp. 401-420
Galium aparine, Impatiens pallida, Parietaria, Pilea pumila, annuals, autumn, biennials, cell walls, death, drought tolerance, flowering, forests, fruiting, growing season, habitats, herbs, indigenous species, leaves, perennials, seeds, spring, stems, turgor, wilting, winter, Wisconsin
Temporal growth patterns and adaptive characters were studied in 17 perennial, 16 annual, and 4 biennial native herbs for one to three growing seasons in dry—mesic, mesic, and wet—mesic forest and in open barrens in southern Wisconsin. In annuals almost all dry matter produced was retained in aerial organs following the initial growth period. Below—ground weight increased rapidly in early season and then slowly increased or declined. In perennials there was a predominantly upward weight movement during growth initiation and during flowering and fruiting and a downward movement between growth initiation and flowering and preceding aboveground senescence or death. Between autumn and spring, all perennials, including wintergreens, lost weight. Most winter annuals increased in both above— and below—ground dry weight over winter, demonstrating maintenance above the compensation point. Growth patterns of biennials in their first year were similar to perennials and in their second year were similar to annuals. Forest herbs lost less water before wilting, were more succulent, wilted in a shorter time, and had heavier seeds than herbs of open habitats. The seeds of the forest annuals were heavier and germinated more readily than seeds of forest perennials. Although most annuals are pioneer, drought—resistant plants, fores annuals wilted easily and were very succulent. This suggests that stems and leaves of the annuals apparently are supported more by turgor pressure, while the perennial plants are supported more by cell wall thickening. This special dependence of annuals on water correlates with their greater numbers in wet—mesic and mesic forests compared with drier forests. Growth characteristics are discussed for eight forest annuals: Amphicarpa bracteata, Ellisia nyctelea, Floerkea proserpinacoides, Galium aparine, Impatiens pallida, Parietaria pennsylvanica, and Pilea pumila.