Peacock Larkspur (Delphinium pavonaceum)

Delphinium pavonaceum is pollinated by bumblebees. In general, bumblebees prefer blue flowers or plants that reflect light in the UV range. It is possible that the white flowers of D. pavonaceum do reflect UV light to attract bumblebees. D. pavonaceum is self-compatible but apparently does not self-pollinate. It needs the insect vector to facilitate pollination. Observations indicate that plants may not flower until after their 5th year. It is difficult to determine how long an individual plant may live, but observations of plants with over 100 flowers indicate that they must have a relatively long life span. Larger plants may emerge and flower one year and be completely absent the next. Like many other larkspurs, D. pavonaceum exhibits this dormancy in response to available moisture (Goodrich 1983)Three threatened larkspurs: Delphinium oreganum, D. leucophaeum, and D. pavonaceum, are all restricted in their distribution to Oregon's Willamette Valley. Delphinium oreganum is intermediate in its floral and inflorescence traits, between the more common blue-flowered D. nuttallii and D. menziesii found in Oregon. Delphinium leucophaeum almost exactly resembles D. nuttallii in form, but its sepals are white instead of blue. D. pavonaceum is similar to D. menziesii in all features except flower color - it has white sepals and blue upper petals instead of blue sepals and white upper petals like D. menziesii. This concentration of rare plants from a single genus in such a limited geographical area raises interesting ecological and evolutionary questions. (Chambers 2000).Chambers (2000) hypothesizes that catastrophic flooding in the Willamette Valley during the Ice Age, between 15,000 and 12,800 years ago, was a catalyst for the evolution of these three rare species. At least 40 times, in roughly 50 year intervals, huge glacier-dammed lakes in Montana formed and broke, inundating over 16,000 square miles in Washington and Oregon. The Willamette Valley was flood-scoured at its north end and filled by a huge temporary lake. Repeated filling and draining of lake created large areas of habitat disturbance. New genetic forms of Delphinium, produced by either hybridization and/or mutation, may have established in these disturbed sites and evolved into the three present day endemic species. Notably, the present ranges of these endemics are limited to the area historically affected by these deluges.Delphinium oreganum appears to have arisen through genetic stabilization of hybridization between D. nuttallii and D. menziesii. In contrast, Delphinium leucophaeum and D. pavonaceum seem to have evolved directly from their respective parental taxa. Isolation through altered pollination behavior by insects, due to the changed flower-color pattern, seems a likely hypothesis in both cases (Chambers 2000). Goodrich (1983) discovered plants that she suspected of being of hybrid origin. These delphiniums have dark purple sepals rather than white ones characteristic of Delphinium pavonaceum. The upper petals are also dark purple, and the plants are morphologically similar to D. pavonaceum. The purple delphinium is only growing among white D. pavonaceum flowers (Karoly personal communication). The presence of what may be an undescribed species growing sympatrically with D. pavonaceum raises concerns about hybridization and the exchange of genetic material between them. Presently, the full impact of hybridization and gene exchange on native plant species is poorly understood. It is possible that genetic material from hybrids may undermine the genetic health and stability of the remaining Delphinium pavonaceum populations (Letter from Karoly to Northway).Turner (1992) examined chromosomes of four Oregon native Delphinium species in order to determine phylogenetic relationships. She found little differentiation between all four species in either the number or morphology of the chromosomes, indicating that there has been little chromosome evolution or it has been parallel in nature. Additionally, chromosome measurements indicated that the purple delphinium of suspected hybrid origin is most closely related to another Oregon species, D. trolliifolium. It can be surmised that D. trolliifolium is likely one of the parent species. Absence of structural heterozygosity in meiotic chromosomes suggests either no introgression (gene exchange), or that the chromosomes of the species are structurally, if not genetically similar. Absence of structural heterozygosity in purple delphiniums suggests that the karyotypes of parent species are similar. Alternatively, recurrent backcrossing may be diluting the hybrid genome. Lastly, the purple hybrid may not be a hybrid. Consistently high levels of seed production and germination among the purple delphinium reveals successful meiosis.Current genetic investigation is comparing chloroplast DNA with nuclear DNA (Mazer 2000). Since chloroplasts are inherited through the female (i.e.. mother) plant, genetic variation can be used to identify the extent of hybridization and the degree of introgression (Letter from Karoly to Northway). In order for genetic markers to be informative, researchers should compare populations of pure color forms. Observation and genetic analysis of one population indicates that it is a pure Delphinium. pavonaceum population, and therefore extremely valuable in determining the impact of hybridization on D. pavonaceum.