WAIT, WHAT, WHERE DID Dichelostemma GO?
By Fred Roberts, CNPS-SD Rare Plant Botanist
A few years ago, I wrote a brief article for the newsletter warning that Dichelostemma capitatum, a name applied to one of San Diego County’s most widely recognized geophytes, bluedicks, was possibly on its way out. If you have seen the newest update to the Jepson e-flora (https://ucjeps.berkeley.edu/eflora) or ventured to use the Jepson Interchange (https://ucjeps.berkeley.edu/interchange), you will see that Dichelostemma capitatum is no longer listed by these sources as the correct name for this plant. It’s official, the name is now Dipterostemon capitatus.
While the new name will take some getting used to (Justin Daniel and I joked yesterday that it does not roll off the tongue like Dichelostemma did), you can be assured there appears good reasons to adopt the new name. If you want to read the full story, you can find it in Robert Preston’s paper, New Nomenclatural Combinations for blue dicks (Dipterostemon capitatus; Asparagaceae: Brodiaeoideae), Phytoneuron 2017-15: 1-11.(http://www.phytoneuron.net/2017Phytoneuron/15PhytoN-Dipterostemon.pdf). It gets a little crazy with the nomenclatural history of the plant. The paper certainly leaves a reader with a good feeling for just how confused the application of various names for this plant have been. Probably only the craziest botany geeks who eat up nomenclatural drama will truly appreciate it.
Without getting into real detail, as most of us probably live confused enough lives trying just to keep the kid and pet namesstraight, I won’t repeat that history here. Suffice it to say, a LOT of names have been applied to this plant since it was first given a name in 1808 (Hookeria pulchellum, if you must know). It is a messy history. It wasn’t always clear how many species wereinvolved (apparently for the longest time, authors recognized two species where there was only one; splitters, you know how they are). And finally, the botanist that got most of the details right when he published the name Dipterostemon capitatus in 1912, had his concept largely forgotten. At least until Preston resurrected it bringing it to the attention of the California botanical community.
Thanks for writing this up for the San Diego CNPS chapter, Fred! For those who bristle at nomenclature changes you might want to know that there’s good reason to move Blue Dicks out of Dichelostemma.
On the genetic side, it has been clear since about 2001 that all the other Dichelostemma species are more closely related to Brodiaea, and that the species now known as Dipterostemon capitatus branched off earlier.
Looking the the flower structure, it was clear to Per Axel Rydberg in 1912 that the six fertile stamens in Blue Dicks made it quite distinct from the three fertile stamens (and generally, three infertile staminodes) in Dichelostemma and Brodiaea. Despite that, it took a further century for botanists to agree that the superficial similarity between Blue Dicks and Ookow was not enough to keep them in the same genus.
In the San Diego area, people are generally going to encounter the "nominate subspecies" D. capitatus subsp. capitatus. (Certainly the Sacramento Valley endemic, D. capitatus subsp. lacuna-vernalis, aka Vernal Pool Blue Dicks, is not a possibility.) However, observations from the eastern part of San Diego County (e.g. around Anza Borrego) have occasionally been identified as D. capitatus subsp. pauciflorus (Few-flowered Blue Dicks).
D. capitatus subsp. pauciflorus is native to the Mojave and Sonora deserts and is characterized by:* pale bracts below the umbel, sometimes streaked with purple (as opposed to dark purple bracts in subsp. capitatus)* 2–5 flowers per umbel (subsp. capitatus can also have as few as 2, but more commonly ranges from about 5 up to 16 or more)* long pedicels on each flower (6–35 mm, and longer than the bracts, whereas in subsp. capitatus they’re usually shorter than the bracts at 2–12 mm).
In reality, there quite a few plants that straddle the criteria between subspecies capitatus and pauciflorus, e.g. with long pedicels, but more than 5 flowers, and indeterminate bracts. This probably indicates that the species has more genetic diversity than is accurately described by the current three subspecies. That’s not a big surprise, given that 18 Brodiaea species and four Dichelostemma species have evolved in the time since that lineage split with the ancestor of Blue Dicks. The species is a good candidate for someone to combine morphometric and phylogenetic research to accurately tease out the distinct taxa and determine how best to identify them. Meantime, we’ll just have to make our best judgment using the Jepson key: https://ucjeps.berkeley.edu/eflora/eflora_keys.php?key=108598