Dipterostemon is a monotypic genus previously included in Dichelostemma native to the Western United States (Oregon, California, Utah, Arizona, New Mexico) and northwest Mexico. It is considered by some to be a member of the Themidaceae family. The Angiosperm Phylogeny Group III placed this family into Asparagaceae as of 2009 but the Jepson eFlora continues in 2021 to list it in Themidaceae. Its only species is Dipterostemon capitatus. In this paper Robert Preston proposed removing this species to an earlier name. In 2021 this name is accepted by Plants of the World Online, the Jepson Manual, and iNaturalist. The Flora of North American and World Flora Online continue to recognize Dichelostemma capitatum. Dipterostemon differs from the other species in Dichelostemma by having 6 stamens instead of three. Three subspecies are recognized. Corms are edible and were eaten by native populations who harvested the larger corms and replanted the cormlets.
Dipterostemon capitatus (Benth.) Rydb., syn. Dichelostemma capitatum (Benth.) Alph.Wood, is known by the common name of Blue Dicks. Capitatus, capitata and capitatum are the masculine, feminine and neuter forms of the Latin word for "having or forming a head". Three subspecies are recognized in 2021. Changes in the name and additional subspecies plays havoc with photos previously on the wiki named Dichelostemma capitatum as keys often require information not readily apparent in a photo (like size of filaments, perianth, pedicels, color of bracts, sometimes corms, height, etc.) And it is often difficult to learn the provenance of plants in cultivation. So this is our best guess for which subspecies are illustrated by previous photos.
Photos 1-3 by Bob Rutemoeller show the flowers in the middle of a Lupine and then alone where the leaves are shown as well. Another view shows the tube. Photos 4-5 were taken by Mary Sue Ittner. The last photo shows it flowering in front of Watsonia coccinea.
Photos 1-2 by Nhu Nguyen shows the vigorous root system of the plants. The thickened part of the root in photo 2 will eventually be consumed by the developing corm. Photo 3 by M. Gastil-Buhl shows corms grown by Jim Duggan on a 1 cm grid.
Dipterostemon capitatus ssp. capitatus is highly variable and widespread in Oregon and throughout the California Floristic Province in California. In coastal California (also Oregon and northern Baja California), Dichelostemma capitatum ssp. capitatum is likely the correct ID. When it comes to California's Mojave Desert and Sierra Nevada there is an overlap between this subspecies and ssp. pauciflorus.
In April of 2015, Travis Owen came across a large colony of Dipterostemon capitatus at the side of the road in Rogue River, Oregon. Photos below were of the colony, on a steep bank with Ceanothus, Toxicoscordion, and Arbutus trees surrounding the patch.
In order to illustrate the natural variation by locality of these plants in California, they are listed by county, loosely north to south:
Dipterostemon capitatus ssp. lacuna-vernalis (L.W. Lenz) R.E. Preston, vernal pool blue dicks, is endemic to the western base of the Sierra Nevada foothills and adjacent Great Valley, ranging from Butte County south to Merced County at elevations between 30 and 270 m. It is found in open upland grasslands adjacent to vernal pools or in grassy swales in oak woodland. It is distinguished from the other two subspecies by having a scape less than 20 cm and a perianth tube under 4 mm. The outer perianth lobes are wider than the inner set of lobes. Photos from iNaturalist taken by natomapaul and Naresh Sukumar in March near Orangevale, California and shared under a CC BY-NC license. Last photo taken by Vince Scheidt.
Dipterostemon capitatus ssp. pauciflorus (Torr.) R.E. Preston, syn. Dichelostemma capitatum ssp. pauciflorum (Torr.) Keator, occurs in desert habitats of the southwestern United States (Arizona, California, Nevada, New Mexico, Utah) and in Northern Mexico. Besides the difference in where it grows, it is distinguished from ssp. capitatus by white or streaked purple instead of dark blue or purple bracts at the tops of the stem and flowers that grow on much longer pedicels (6-34 mm vs. 2-12 mm). There are also only 2-5 flowers in the average umbel. In ssp. capitatum there are 2-16. The two photos below were taken by Nhu Nguyen at a rock outcrop outside of the town of Onyx on the western edge of the Mojave Desert. A few of the plants had interesting and long pedicels. Photos above also taken near that spot listed under Kern County did not have the long pedicels raising interesting questions about the subspecies designation. Subspecies were generally not recognized in the later years when this plant was considered Dichelostemma capitatum.
Photo below from iNaturalist taken by wirich in Arizona in April and shared under a CC BY-NC license.