Bluedicks confusion

For some time I've been blithely marking observations of bluedicks (a name which induces tittering among elementary school students on field trips, encouraging the use of the alternate common name "desert hyacinth" with that audience) as Dichelostemma capitatum. Correct, as far as it goes, but there are two subspecies, capitatum (the nominative subspecies) and pauciflorum. Only the latter is found in Arizona. Unfortunately, the SEINet range map has a sizeable number of Arizona collections labeled as ssp. capitatum. As I explained here:

"There's a large number of specimens labeled Dichelostemma capitatum ssp. capitatum on the SEINet range map. All of these were originally identified as either Dichelostemma pulchellum (the vast majority) or Brodiea capitata. When the names of these two taxa were updated to D. capitatum in the SEINet database they were assigned to the nominative subspecies. Oops. FNA has accurate distribution maps of the subspecies capitatum and pauciflorum."

I've been trying lately to be sure to add subspecific names where known or where identifiable, because occasionally a subspecies or variety is "promoted" to species or otherwise renamed.

(Thanks to @rupertclayton for tipping me to the subspecies issue.)

Publicado el miércoles, 26 de febrero de 2020 a las 10:13 PM por stevejones stevejones

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Thanks for posting this to explain the existence of subspecies for Dichelostemma capitatum.

It does seem pretty certain that any observation in Arizona (or Nevada, Utah or Sonora, MX) is necessarily Dichelostemma capitatum ssp. pauciflorum (Few-Flowered Blue Dicks). It can be distinguished from D. c. ssp. capitatum by its involucre of pale (rather than dark blue/purple) bracts at the top of the stem and flowers that grow on much longer pedicels (6–35 mm vs. 2–12 mm), with the pedicels typically longer than the bracts. There are also fewer flowers in the average umbel (2–5, whereas D. c. ssp. capitatum has 2–16).

In coastal California (also Oregon and northern Baja California), we can be pretty sure that Dichelostemma capitatum ssp. capitatum is the right ID. When it comes to California's Mojave Desert and Sierra Nevada, we need to take a little more care to distinguish subspecies. It appears that the ranges for capitatum and pauciflorum abut or overlap in the Mojave, and it will be interesting to see what iNat observations tell us about distribution there.

In the Sierra foothills and along the eastern edge of the San Joaquin and Sacramento valleys there's a third subspecies to consider, Dichelostemma capitatum ssp. lacuna-vernalis, which "is endemic to the western base of the Sierra Nevada foothills and adjacent Great Valley, ranging from Butte County south to Merced County." Although it's named after the vernal pools of this region, it doesn't actually grow in the pools themselves, "but in open upland grasslands adjacent to vernal pools, often on mounds, or in grassy swales in oak woodland." Compared to the other two subspecies lacuna-vernalis has a shorter scape (<20 cm), a perianth tube under 4 mm (being much shorter than the lobes), and outer perianth lobes that are wider than the inner set of lobes.

Dichelostemma capitatum ssp. lacuna-vernalis was first described by Lee Lenz in 1974, but wasn't accepted by some later researchers. However, work by Robert E. Preston in 2014 has established that it really is a distinct subspecies. So far, no observations on iNat are identified as this subspecies. There probably are quite a few, but it may take some careful examination to tease them out from the ssp. capitatum observations which occur fairly nearby.

There are several more wrinkles to the taxonomy of this species. Firstly, there appears to be agreement that there are likely other subspecies hiding within its considerable morphological variety. Phylogenetic and morphometric analysis may be able to provide guidance so long as researchers can get funding to do this work. A complicating factor is the effect of thousands of years of human interaction with the species. The bulbs are edible and plants were managed by Native American communities as a reliable food source. While most management would have been within a particular patch, it's possible that corms from were moved among sites at times.

Lastly, the relationship to other species in the genus appears likely to change. Observers often have trouble telling Dichelostemma capitatum from the superficially similar Dichelostemma congestum and Dichelostemma multiflorum. In fact, there are quite a few morphological differences, and a 2017 paper by Robert Preston laid out the case for the species to be moved to a whole new genus as Dipterostemon capitatus. This change has now been reflected in the Jepson eFlora treatment of Dipterostemon capitatus separately from its former sister species in Dichelostemma. The change has not yet propagated to the Flora of North America or Plants of the World online, so iNat users should continue to ID these plants as Dichelostemma capitatum. When the change occurs, existing observations will be moved to their new names automatically.

Sources:

Preston, R.E. 2014. Vernal Pool Blue Dicks (Dichelostemma lacuna-vernalis;
Asparagaceae: Brodiaeoideae) Revisited. Madroño, 61(4) 350–366. https://www.jstor.org/stable/43289063

Preston, R.E. 2017. New nomenclatural combinations for blue dicks (Dipterostemon capitatus; Asparagaceae: Brodiaeoideae). Phytoneuron 2017-15: 1–11. http://www.phytoneuron.net/2017Phytoneuron/15PhytoN-Dipterostemon.pdf

Anotado por rupertclayton hace cerca de 4 años

Excellent, thanks for that deeper and more complete dive, Rupert. I read Preston's Dipeterostemon paper earlier in the week and it looks good. Yes, when that change occurs, the new nomenclature will be updated automatically (well, after a curator makes the change). It can be frustrating to know the change has been made and not gravitate to it immediately, but them's the rules. Always remember, "thank goodness for synonymy."

Anotado por stevejones hace cerca de 4 años

Very thankful for your expertise @stevejones and @rupertclayton !

Anotado por ezpixels hace cerca de 4 años

Thank you for such an excellent update. This is a common species in my area of observations.

Anotado por lonnyholmes hace cerca de 4 años

Thanks @rupertclayton! This CalPhoto by Robert Preston (https://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+0000+0115+0163) shows how much narrower the inner petals are on D. capitatum ssp. lacuna-vernalis.

Anotado por jimtietz hace casi 4 años

Interesting discussion, especially concerning the differences between ssp. capitatum and ssp. pauciflorum. The anthropogenic spread of this species shouldn't be underestimated, which explains some anomalies in distribution. Definitely makes it a challenge to know what is indigenous and what is naturalized. Two examples:
https://www.inaturalist.org/observations/62076167
https://www.inaturalist.org/observations/39331640
My suspicion is the the latter (at least) was naturalized on this island because there are no nearby records to the best of my knowledge.

Anotado por snakeinmypocket hace casi 3 años

Good points @snakeinmypocket. I agree that pre-European human cultivation is likely the origin of Blue Dicks on many Pacific coastal islands.

Edward Lee Greene actually described the Blue Dicks plants growing on the islands of Southern California and Baja California as a separate species (Brodiaea insularis) in 1886 on account of their much larger size (scapes 3-5 ft tall, leaves 3 ft long). He mentioned that corms collected from Isla Guadalupe and grown at U.C. Berkeley flowered many weeks later than other Blue Dicks plants.

In 1912, Per Axel Rydberg described the new genus Dipterostemon for Blue Dicks on the basis of its six fertile stamens and placed within it four species (including insularis) all now regarded as Dipterostemon capitatus of some sort. Sadly, this didn't find acceptance and the botanical community went back to using Brodiaea and Dichelostemma for these plants.

In December 1918, J. Francis MacBride reduced this island taxon to a variety of Brodiaea capitata based on the distinction between insularis and capitata being only one of size.

Ultimately, even the island variety was synonymized by Robert Hoover in "The Genus Dichelostemma" in 1940. He lists Greene, Rydberg and MacBride's taxa as synonyms of Dichelostemma pulchellum and says:

Particular mention should be made of Brodiaea insularis Greene, a variant occurring islands off the coast of southern California and northern Baja California. This plant seems to differ from typical D. pulchellum only in having very tall scapes and very large leaves. Field observations lead me to believe that these differences are without taxonomic significance. In favorable situations, such as fertile creek bottoms, and in seasons with favorable weather conditions, plants of the mainland may sometimes grow as large as any of the specimens seen from the islands. There is probably a genetic basis for the size of the insular plant, but since the same form may apparently be produced under the direct stimulus of environment, segregation on such a basis does not seem desirable.

There has also been some interesting research on the use of Blue Dicks corms for food and their presence at archaeological sites. This paper uses the seasonal changes in the corm to draw some conclusions about harvest times on Santa Cruz Island.

Gill, Kristina. (2014). Seasons of Change: Using Seasonal Morphological Changes in Brodiaea Corms to Determine Season of Harvest from Archaeobotanical Remains. American Antiquity. 79. 638-654. 10.7183/0002-7316.79.4.638.

Anotado por rupertclayton hace casi 3 años

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