Some Aspects of the Autecology of Prairie Larkspur (Delphinium virescens) in Tennessee Cedar Glades

Abstract

Disjunct populations of the prairie larkspur (Delphinium virescens Nutt.) occur in disturbed and relatively undisturbed plant communities in the middle Tennessee cedar glades. Field observations on its ecological life cycle in cedar glades were carried out over a 3-year period, and laboratory investigations were conducted on seed germination, bud break, production of new absorbing roots and flowering. The active part of the life cycle of this herbaceous, polycarpic perennial occurs during autumn, winter and spring, commencing with seed germination, bud break and production of new absorbing roots in late September and October. In autumn, seedlings produce 1-2 leaves, and older plants form rosettes with few-many leaves. Flower buds are formed on reproductively mature plants in March, and bolting begins in late April. Low winter temperatures are prerequisite for bolting and flowering. By midto late May the plants are in full flower, and by mid-June most of the seeds are matured and dispersed. Senescence of shoots and absorbing roots occurs in all plants during late May and June; in mature plants, senescence accompanies fruit and seed maturity. By the time the shoots are dead, small perennating buds have been formed on the caudex at the base of the old shoot. Although neither buds nor seeds are innately dormant during the summer, they are prevented from initiating growth by high temperatures. Growth of seedlings and juveniles is slow and plants are several years old when they reach reproductive maturity in the field. The life cycle behavior of D. virescens is an adaptation of this droughtintolerant, cold-resistant perennial to cedar glades and prairies. INTRODUCTION D. virescens Nutt. is a herbaceous perennial that occurs in prairies, plains, barrens and dry open woods (Fernald, 1950; Gleason and Cronquist, 1963) from northwestern Wisconsin to Manitoba and North Dakota S to Illinois, Tennessee, Georgia, Louisiana, Texas, New Mexico, 'Colorado and Arizona (Ewan, 1945; Fernald, 1950; Gleason and Cronquist, 1963; Baskin, et al., 1968). In Tennessee it is restricted to the Central Basin where it is closely associated with cedar glades (Baskin et al., 1968). The purpose of this study was to make phenological observations on plants of this species growing in the middle Tennessee cedar glades and to carry out laboratory studies on the temperature and/or water relations of root growth (production of new absorbing roots), bud break, flowering and seed dormancy and germination. This study is a part of a broader investigation of the ecological life histories of the principal higher-plant species occurring in cedar glades. CEDAR GLADE HABITAT AND PLANT ASSOCIATES Cedar glades of central Tennessee are open, nonforested areas with shallow soils that are developed on both thinand thick-bedded Ordovician limestones. The most extensive glades are on exposures of