Plant Species of the Borrego Desert:
Loasaceae: Mentzelia species, Blazing Stars
Loasaceae: Mentzelia species, Blazing Stars
This page was just begun on 2 February 2026, primarily to hold pictures of some of our species. This page is still being worked on, with more info to come. Links from the pix are not yet in place, nor are photo credits.
Even though the common name of M. albicaulis is white-stemmed blazing star, from the scientific name, white stems are not confined to M. albicaulis; the other two species can also have white stems. See, for example, the fourth pix here, and the last three pix here of M. desertorum, and this post and this post of M. affinis.
| M. affinis | M. albicaulis | M. desertorum |
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| Fig. 1. Top: side view of the flowers of three Mentzelia species shown to scale. Note that the ovary of M. affinis is about the same width from top to bottom, reflecting its one row of ovules / seeds, whereas the ovaries of the other two species are wider near the petals, reflecting their ~three rows of ovules / seeds.
Middle: frontal view of the flower shown to scale, but using a slightly larger scale than in the side view. The measured size of the corolla width, from petal tip to petal tip, is 14 mm for M. affinis; 11 mm for M. albicaulis; and 5.5 mm for M. desertorum. Note the brown sepals (seen in-between the petals) of M. desertorum and the very short brown tips of the sepals of M. albicaulis. I don't know if this coloration is just a stage in the development of the flower, or somewhat diagnostic. | ||
| M. affinis |
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| M. albicaulis |
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| M. desertorum |
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| Fig. 2. Basal rosette leaves of the three Mentzelia species shown to scale. Leaves can change remarkable once a stem is produced, so cauline leaves can be quite different, and variable. Even the basal leaves can vary; see the next three figures.
The leaf length in these pix is 51 mm for M. albicaulis; 68 mm for M. affinis; and 56 mm for M. desertorum. | |
Some of the variation in the basal rosette leaves of these three Mentzelia species are shown in the next three figures.
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| Fig. 3. Variation in basal rosette leaves of Mentzelia affinis, not necessarily to scale. The four pix for M. affinis are all from the Henderson Canyon Road Flower Fields. The first pix is from Tom Chester; the other three pix are from Kate Harper. | |
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| Fig. 4. Variation in basal rosette leaves of Mentzelia albicaulis species, not necessarily to scale. | |
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| Fig. 5. Variation in basal rosette leaves of Mentzelia desertorum, not necessarily to scale. | |
The Mentzelia key relies on the number of rows of seeds in the fruit to distinguish M. affinis from the other two species, and the shape of the seeds. These two characteristics are directly related, since if there is just one row of seeds, they will be prism-shaped, filling the inside of the fruit. But if there are three rows of seeds, each will be grain-like, in order to fit together inside the fruit.
Fortunately, one doesn't need mature fruit to verify the number of rows of seeds. The ovules in the ovary in flower are already in one row or three rows. See Fig. 6.
| M. affinis | M. albicaulis |
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| Fig. 6. Left: The ovules of M. affinis are in one row, with the exception of the ovules closest to the petals, and already have a prism shape. Right: The ovules of M. albicaulis are in ~3 rows, packed closely together, and are already grain-like in shape. There has been some disturbance to the ovules in the process of opening up the ovary, which has moved some of the ovules from their original position. (I used a dissecting needle to split it open; I should have used a razor blade or exacto knife like Keir Morse did in his third pix in this observation. | |