Boltonia decurrens

Daisy-like inflorescences composed of perfect yellow disk flowers and white to pale violet pistillate ray flowers; strongly decurrent leaves; lack of rhizomes. Boltonia asteroides var. recognita has decurrent leaves and lacks rhizomes, and also has a strong tendency to have larger flowers, more frequently with violet colored rays (Schwegman and Nyboer, 1985).

Colonizes periodically disturbed riverine moist soil habitats (Smith et al. 2005). In general, sites where the species is successful in reproducing sexually and maintaining a self-sustaining population are characterized by moist, sandy soil and regular disturbance, preferably periodic flooding, which maintains open areas with high light levels. Analysis of 19th-century habitat data taken from herbarium sheets indicates that natural habitat was the shores of lakes and the banks of streams, including the Illinois River. In these habitats, regular flooding prevented succession, allowing sunlight to reach the seedlings. Boltonia decurrens is still found in these occasional natural habitats, but it is now primarily restricted to disturbed lowland areas, where it appears to be dependent on human activities (mowing, cultivation) for survival. Germination and seedling establishment do not occur where the soil surface is shaded, such as in places where natural succession has been uninterrupted for a period of 3-5 years. Seed germination is also inhibited by silt deposition.

Boltonia decurrens blooms from August through October throughout its range (Schwegman and Nyboer, 1985). Little variance has been noted in time of anthesis for populations from different locations; however, there is a great deal of variance in the size of plants at anthesis. Plants which have overwintered (either seedlings or vegetatively-produced rosettes) are generally >1.5 m when flowering is initiated, as compared to seedlings which germinate in spring and flower in late summer of the same year (flowering individuals have been noted which were <0.5 m in height). Anthesis does not appear to be related to either photoperiod or temperature at the time of flowering but occurs in response to bolting, which in rosettes, at least, is dependent upon pre-treatment with low temperature. In any given cohort, some seedlings will bolt and flower without cold treatment and some do not flower until they have overwintered. The mechanism for these differing responses is unknown (Smith, 1991).

Both seedlings and vegetatively-produced rosettes can withstand prolonged periods of flooding (Stoecker, Smith and Melton, 1995), and have been observed to develop while completely submerged, to bolt above water level, flower and produce seeds (Smith, 1990). Seeds are conditionally dormant (Baskin and Baskin, 1988), with freshly-produced seeds germinating at warmer temperatures (30C) and those which have after-ripened germinating at a wider range of temperatures (10 - 30C). Peak germination appears to be in spring (Smith, 1991). Seeds stored in a refrigerator at 4C for 6 years are still viable (ca. 50% germination percentage), and a recent study indicates that in the field seeds remain viable in the soil for at least two years (Smith, 1994). In spite of its threatened status and restricted range, preliminary isozyme data developed by Thomas Ranker (University of Colorado, Boulder) from seeds collected from three populations in Illinois in 1994 indicate that there is a high level of genetic diversity (Smith, 1995). This rare species is much more variable, by all the measures examined, than most rare or geographically-restricted plant species, and is even slightly more variable than the average plant species regardless of rarity, distribution, or a variety of other life-history characteristics (Hamrick and Godt, 1990).

Achenes float and are often dispersed by flowing water (Baskin and Baskin 2002).

Vegetative reproduction occurs through shoots formed from a basal rosette (Smith and Keevin 1998).
The species is primarily outcrossing, but some selfing occurs (Smith, 1995). Pistillate ray flowers and perfect disk flowers produce morphologically distinct achenes in inflorescences of approximately 350 flowers in a 1:5 ray to disk ratio. Seed production is prolific with an average of ca. 50,000 seeds produced per plant (Smith & Keevin 1998; Smith, 1990). Germination is ca. 60% under laboratory conditions (Smith, 1990), but seedling survival in the field is <1%. However under optimal conditions, the average plant produces 40,000 seedlings but the rate of seedling survival is low (Smith & Keevin 1998). In late fall, as each flowering individual dies, leaving no persistent root stock, basal rosettes develop independent root systems. The rosettes overwinter, bolt the following spring and flower.