False-rue anemone COSEWIC assessment and status report: chapter 6
Biology
Physiology
Flowering begins when temperatures are suitable for plant growth and pollinator activity and ends before closure of the canopy (Schemske et al., 1978). In Ontario and Illinois (Melampy and Heyworth, 1980) Enemion biternatum flowers in late April or May and is in fruit by early June. Flowering occurs earlier in the south. For example, in central Kentucky flowering begins in mid-March and continues until early May, with peak flowering in late March or early April (Baskin and Baskin, 1986). Flowering times of Enemion biternatum are earlier in warmer weather and can be postponed in colder temperatures (Schemske et al., 1978). Flowering lasts 7-10 days of which 3-4 days are in the female phase (flower stigmas are receptive before the anthers open; see Schemske et al., 1978). Delayed flowering peaks can be detrimental to seed set of Enemion biternatum (Schemske et al., 1978).
In Ontario, seeds mature by early June. Seeds have no known special means of dispersal (Schemske et al., 1978). Leaves begin to turn yellow or brown as seeds ripen and by early to mid-June all have senesced (Baskin and Baskin, 1986). In central Kentucky new leaves emerge in mid-September, remaining green all winter and a few plants may flower in the autumn. By early March, winter leaves have turned red and new spring leaves emerge (Baskin and Baskin, 1986). Autumn flowering has not been observed in more northerly areas (Austen, 1990).
Enemion biternatum is a hermaphrodite (both male and female organs within the same flower) and grows in clumps that probably represent clones (Melampy and Heyworth, 1980). Enemion biternatum is self-compatible but not autogamous (self-pollination within a single flower); autogamy appears to be prevented by protogyny with stigmas becoming non-receptive by the time the anthers dehisce (Melampy and Hayworth, 1980). Melampy and Hayworth (1980) found that Enemion biternatum plants were geitonogamous 26% of the time, outcrossed within a patch 16% of the time and outcrossed between patches 28% of the time. Geitonogamous pollination, the transfer of pollen between flowers on the same genetic individual, has potential consequences such as increasing the potential for self fertilization, which can result in inbreeding depression, or reducing reproductive success due to a reduced amount of pollen outcrossing to other individuals.
Reproduction/dispersal
Enemion biternatum is entomophilous (pollinated by insects). No nocturnal pollinators were seen by Melampy and Hayworth (1980) on Enemion biternatum. This is probably related to the cool nights during early spring when this species flowers. A variety of insects have been found visiting Enemion biternatum flowers (Apis mellifera, andrenid bees, halictid bees, syrphid flies, other flies and beetles). However, the rate of visitation of these pollinators is low even when Enemion biternatum is in flower. Enemion biternatum is a nectar-less plant and is not a preferred resource for insect pollinators when the nectar-bearing flowers of plants such as Claytonia virginica and Cardamine concatenata (Dentaria laciniata) are nearby (Melampy and Hayworth, 1980). Nectar-less plants may receive insect visits by extending their flowering season to include intervals when few nectar-producing plants are flowering. This strategy may be employed by Enemion biternatum (Melampy and Hayworth, 1980).
The key to maximizing seed set for Enemion biternatum is maintaining low flower availability per unit time and extending the flowering season to include gaps between or after flowering periods of other sympatric species. Maximum seed set for Enemion biternatum occurred after the peak of flowering for Claytonia virginica, suggesting that as preferred species decrease in abundance, insects began visiting Enemion biternatum more often and pollinating more Enemion biternatum flowers (Melampy and Hayworth, 1980). The low visitation rate of pollinators to Enemion biternatum plants suggests that Enemion biternatum may rely on mistakes by foraging insects that visit its flowers while searching for those of other species. Mistakes may increase or insects may be forced to visit Enemion biternatum occasionally as preferred species decline in abundance. Therefore a lack of pollinator availability could limit seed production in Enemion biternatum (Melampy and Hayworth, 1980). There is some evidence that wind plays a role in the pollination of Enemion biternatum. For example three of 37 flowers covered with nylon screen produced seed in a field study conducted by Melampy and Hayworth (1980).
In a field study examining the phenology of Enemion biternatum in Illinois, peak seed set was achieved by flowers that were open during peak flowering in 1975, and in flowers blooming just prior to peak flowering in 1976 (Schemske et al., 1978). Therefore, it appeared that perfect timing of flowering in this species is seldom achieved (Schemske et al., 1978).
Enemion biternatum seeds collected from central Kentucky were sown in soil and placed in a non-heated greenhouse (Baskin and Baskin, 1986). Seeds exhibited embryo growth and completed germination (emerged radicle and cotyledons) in the autumn (Baskin and Baskin 1986). Embryos grew slowly during the summer but elongated rapidly in early September; seeds germinated in October (Baskin and Baskin, 1986).
Germination of Enemion biternatum is similar to that of species exhibiting epicotyl dormancy (i.e., radicles are dormant and require a period of warm stratification during the summer before they emerge at favourable autumn temperatures) because radicle emergence occurs in the autumn. However, cotyledons also emerge from seeds of Enemion biternatum in autumn whereas in species with epicotyl dormancy the seed with an emerged radicle must be cold stratified during the winter for the cotyledons to emerge (Baskin and Baskin, 1986). Before seeds of Enemion biternatum can germinate, embryos must elongate from less than 0.2 mm to more than 1 mm. Optimum temperatures (day/night) for germination of freshly matured seeds were 20/10 degrees Celsius. Seeds eventually germinated at 30/15 degrees Celsius and 25/15 degrees Celsius (Baskin and Baskin, 1986). Embryos are non-dormant and seeds of Enemion biternatum require a long time at high temperatures to complete embryo growth and germinate (Baskin and Baskin, 1986). Laboratory studies suggest that exposing seeds of Enemion biternatum to high summer temperatures may enhance germination at early autumn temperatures (Baskin and Baskin, 1986).
The germination pattern of Enemion biternatum differs from that of all other perennial herbs of mesic deciduous forests studied to date. Most forest species are deeply dormant and complete germination in spring. Enemion biternatum is non-dormant and completes germination in autumn (Baskin and Baskin, 1986). To date, germination patterns of Enemion biternatum in Ontario have not been examined (Austen, 1990).
Enemion biternatum seedlings produced in the autumn may have a much longer period for establishment and growth before the onset of dormancy in June than if germination was delayed until spring. Therefore, Enemion biternatum may require less time from seed dispersal to reproductive maturity than plants developing from seeds that germinate the following spring. There may, however, be a disadvantage to passing the winter in a seedling versus seed stage (Baskin and Baskin, 1986).
Comprehensive studies have not been conducted on the demography, phenology and reproductive ecology of Enemion biternatum in Ontario (Austen, 1990). Enemion biternatum is a perennial with considerable vegetative propagation and therefore this may diminish to some extent the importance of high seed production in any one year (Schemske et al., 1978). Abundant seeds were produced in plants observed in Elgin County during early June. It is not known when germination occurs in the field in Ontario. Populations in Ontario vary from small patches, less than 1 x 1 m (approximately 50 plants), to large areas of forest that are covered with plants, numbering in the thousands (Austen, 1990).
Interspecific interactions
No information was found regarding competitive or interspecific interactions that affect Enemion biternatum populations. The population ecology of Enemion biternatum in Ontario remains unstudied.
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