Arctostaphylos glauca, Bigberry Manzanita
I've started classifying the iNat observations of Arctostaphylos glauca in the Borrego Desert area into plants with glabrous twigs, plants with short-hairy twigs, and plants with glandular twigs. I've started with the easternmost observations, and have done the first 100 observations, everything east of -116.60°. The co-authors of this analysis provided most of the correctly-identified A. glauca observations with good enough photographs that could be used for this analysis.
The vast majority of most plants of A. glauca have glabrous twigs. But in one location along the California Riding and Hiking Trail north of S22 / Jasper Trail, half the plants in a population of about 30 or so plants have short-hairy twigs! They are otherwise clear A. glauca, with no burl, glaucous leaves, and a typical A. glauca nascent inflorescence. Similar plants are found in the Pinyon Ridge area.
There are also a scattering of A. glauca plants in various locations that have what appear to be glandular trichomes on the stem, consisting of short, stubby, multicellular trichomes, that may or may not actually have glandular goo inside them. They have been found in four different areas so far.
Table 1 gives links to iNat observations for plants with short-hairy twigs. Table 2 gives links to plants with glandular twigs.
Table 1. Links to iNat observations of A. glauca plants with short-hairy twigs
| Location | Link to iNat | Notes |
|---|---|---|
| CA Riding and Hiking Trail | At S22 | Plant has some hairy twigs, and some glabrous twigs |
| CA Riding and Hiking Trail population 0.4 miles north of S22 | Plant 1 | |
| CA Riding and Hiking Trail population 0.4 miles north of S22 | Plant 2 | |
| CA Riding and Hiking Trail population 0.4 miles north of S22 | Plant 3 | |
| CA Riding and Hiking Trail population 0.4 miles north of S22 | Plant 4 | |
| Pinyon Ridge | Plant 1 | |
| Pinyon Ridge | Plant 2 | |
Table 2. Links to iNat observations of A. glauca plants with glandular twigs
| Location | Link to iNat | Notes |
|---|---|---|
| Pena Spring | The plant found by Henrik Kibak that started this work | |
| Pena Spring | Follow-up on Henrik's plant | |
| S22 just west of Jasper Trail | Plant 1 | |
| Pinyon Ridge | Plant 1 | |
| Pinyon Ridge | Possibly has glandular twigs; needs follow-up | Pix do not have enough resolution. It is unclear whether what look like glands are just a resolution artifact. |
| PCT north of S22 | Plant 1 | |
Some older stats that need a small amount of updating:
Of those 100 iNat observations from all observers, 50 were actually of A. glauca and had good enough photographs to discern twig hairs if present. Of those 50, 36 have glabrous twigs; 9 have short-hairy twigs; and 5 have glandular twigs.
Of the remaining 50 observations, 34 observations do not have a good enough photo of the twigs to categorize them, and 16 observations were not actually of A. glauca.
Fig. 1 plots the locations of all iNat observations of A. glauca, with separate symbols for those for which I could classify the twig trichomes.
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| Fig. 1. Left: Map of A. glauca forms. The small blue rectangles without an overlaying symbol represent observations without a good enough photograph of a twig to classify it. Right: Reference map from iNat to show names for the geographic locations. Note that this iNat reference map has many more A. glauca observations than it does now at iNat after I went through them and redetermined observations that were not definitely A. glauca. | |