Plant of the Week
Scarlet Gilia (Ipomopsis aggregata)
By Walter Fertig
Scarlet gilia or skyrocket has been known to modern science since 1806, when western explorers Lewis and Clark collected the first specimen along the Lolo Trail in the mountains of northern Idaho. This is a striking plant, with bright green, comb-like leaves and an elongated inflorescence of red, pink, or white flowers. Each flower forms an elongated tube that bursts into five spreading corolla lobes at the tip. Surprisingly, taxonomists have had a difficult time deciding just what scientific name to give it. Starting with the original name of Cantua aggregata given by Frederick Pursh, scarlet gilia has been assigned to no fewer than eight different genera in the phlox family (Polemoniaceae). Extremely variable across its broad range (southern British Columbia to Montana south to northern Mexico), taxonomists have named at least 27 different forms of scarlet gilia as separate species. Today, these are all recognized as just one to three species (again, depending on the taxonomic treatment) with 7-10 different subspecies. Most authorities now know the species as Ipomopsis aggregata (Ipomopsis comes from Greek words for “striking appearance”), though older books often treat it as Gilia aggregata (for Spanish botanist Felipe Luis Gil).
Much of the taxonomic confusion surrounding scarlet gilia is due to differences in flower color among populations. The plant’s long, narrow floral tube is well suited for pollination by long-beaked or long-tongued animals, especially hummingbirds and moths. Red-flowered races of scarlet gilia tend to be pollinated mostly by hummingbirds, which are especially attracted to the color red because of their outstanding vision. White flowers are more attractive to moths that visit the gilia flowers at dusk or nighttime and are drawn by the flower’s unpleasant scent. Scarlet gilia blooms over much of the summer and in some populations blossoms that emerge from May to July are red and hummingbird pollinated, while flowers that mature later in July and August are white and pollinated by moths. This color shift can even be observed among different flowers on the same plant.
Scarlet gilia grows in a variety of habitats, from desert canyons and cliffs to montane meadows, and subalpine rock fields. These plants are relatively short-lived and often die after flowering. In many instances, individuals will persist for one to several years in rosette form, consisting only of a basal clump of deeply pinnately lobed leaves. Flowering stalks are highly edible to native wildlife and livestock, but plants can compensate for herbivory by sending up new shoots and branches.