Dudleya arizonica, Arizona chalk dudleya

and

D. saxosa ssp. aloides, desert dudleya

Fig. 1. Left: Dudleya arizonica, Arizona chalk dudleya, Kate Harper, Rainbow Canyon, 4/6/12. Right: D. saxosa ssp. aloides, desert dudleya, Mike Crouse, Rockhouse Canyon, 2/5/09. Click on the pictures for larger versions.

There are just two Dudleya species in the Borrego Desert: Dudleya arizonica, Arizona chalk dudleya, and D. saxosa ssp. aloides, desert dudleya.

Both of these have sister species that are very similar at first glance that are found to the west in the coastal and montane portions of San Diego County. D. lanceolata is the sister species of D. saxosa, and these two species are primarily distinguished by differences in the size of the plant, with D. lanceolata larger. D. pulverulenta is the sister species of D. arizonica, and again these two species are primarily distinguished by differences in the size of the plant, with D. pulverulenta larger. For both of these species pairs, where the ranges overlap, it may be difficult to determine a given specimen as either the coastal version or the desert version.

In fact, for some years, Tom was not convinced the desert plants called, at that time, D. pulverulenta ssp. arizonica, were any different from the coastal plants, D. pulverulenta ssp. pulverulenta, since the desert plants looked much more like ssp. pulverulenta than pictures of the Arizona plants of ssp. arizonica, and there was no sharp geographic distinction between them. But he finally was convinced by the difference in the leaf shapes, and in the orientation of the flowers, that there were indeed two extremes that deserved taxonomic recognition.

For an excellent discussion of these species pairs, see the Flora of North America treatment by Moran: D. arizonica and D. pulverulenta; and D. saxosa and D. lanceolata.

Fortunately, in the Borrego Desert we don't have to worry about distinguishing the desert species from the coastal species; we just have the two desert species. And with our two desert species, most of the time, it is very easy to tell at a glance whether a given desert plant is D. arizonica or D. saxosa just from the shape and width of the leaves, and the extent of the chalky center of the leaf rosette. See the first set of pictures below that show the clear differences.

Table 1. ID Comparison Table for Dudleya in ABDSP

CharacteristicD. arizonica
Arizona chalk dudleya
D. saxosa ssp. aloides
desert dudleya
# rosettes per plantgen 11-8
Leaf Shapewidely oblong to oblong-obovate to diamond-shapednarrowly lance-oblong
Leaf width1-7 cm0.6-2.5 cm
Leaf tipgen long-acuminateacute to rounded
Leaf colorLarge portion of innermost leaves glaucousInnermost leaves glaucous only in youth
Pedicel in fruitoften sharply bentnot sharply bent

Pictures illustrating the differences

Click on the pictures for larger versions.


D. arizonica, Arizona chalk dudleya
Kate Harper, Rainbow Canyon, 4/6/12.

D. saxosa ssp. aloides, desert dudleya
Mike Crouse, Rockhouse Canyon, 2/5/09.

D. arizonica, Arizona chalk dudleya
Kate Harper, Rainbow Canyon, 4/6/12.

D. saxosa ssp. aloides, desert dudleya
Kate Harper, Culp Valley, 4/12/11.



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Copyright © 2014 by Kate Harper and Tom Chester.
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Comments and feedback: Kate Harper
Updated 17 January 2014