Plant Species of San Jacinto Mountain: Hieracium albiflorum, white hawkweed, and Hieracium horridum, prickly hawkweed
| H. albiflorum white hawkweed | H. horridum prickly hawkweed |
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| Fig. 1. Flowers and fruit of Hieracium albiflorum (left) and Hieracium horridum (right). The involucre of H. albiflorum is not always long hairy; sometimes it is glabrous or glandular; see another example. The pappus of H. albiflorum can be dull white, as in the photograph, or tan. The head of H. albiflorum in fruit appears to have the innermost phyllaries still present below the seeds.
Click on the pictures for larger versions. | |
Hieracium is essentially a worldwide genus containing about 250 species, with 36 species given in the Flora of North America north of Mexico treatment (FNA); ten species in California; and three species in southern California. We have just two Hieracium species at San Jacinto Mountain, H. albiflorum and H. horridum. H. argutum is the third species in southern California, found in SCo, n ChI, and TR, but not at San Jacinto Mountain.
H. horridum lives only at higher elevations in California, Nevada and Oregon, whereas H. albiflorum is a more widespread species, found at elevations below 9500 feet in Mexico, nearly the entire western U.S., and across Canada.
The name Hieracium comes from the ancient Greek "hierax", meaning "a hawk". Michael Charters reports:
The Roman naturalist Pliny believed that hawks fed on this plant to strengthen their eyesight and thus it became the Greek and Latin name for this and similar plants, the common name of which is hawkweed.albiflorum means "white flowered".
horridum means "very prickly or bristly".
Interestingly, the FNA treatment states:
Most plants referable to Hieracium are apomictic (reproducing from asexually produced seeds). Apomictic reproduction often results in perpetuation of morphologic variants at populational and regional levels. Temptation to name such variants as species has proven irresistible to some botanists; upward of 9,000 species names have been published in Hieracium. Circumscriptions of "species" in Hieracium seem to be more artificial than in most genera of composites.
Fortunately, our two species of hawkweed are fairly consistent morphologically, and they are spectacularly easy to tell apart when they are in bloom, since white hawkweed has white flowers, and prickly hawkweed has yellow flowers; see Fig. 1.
Even without blooms, if there is an old inflorescence, white hawkweed can be recognized by a generally taller inflorescence that is looser (with more separation between the individual flower heads), and with no noticeable leaves in the inflorescence; see Fig. 2.
| H. albiflorum white hawkweed | H. horridum prickly hawkweed |
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| Fig. 2. Habit of blooming plants of Hieracium albiflorum (left) and Hieracium horridum (right). Also see another specimen of H. albiflorum for a photograph of the inflorescence from the side.
Click on the pictures for larger versions. | |
Their habitat differs as well, with white hawkweed growing in shady areas with soil, usually with pine duff. Prickly hawkweed grows in at the base of rocks or in cracks in cliffs. See the backgrounds in Figs. 2 and 3 to see the habitat difference.
The basal leaves of the two species are quite similar, which can make it difficult to determine the species reliably from a single rosette. The differences are subtle; the basal leaves of H. albiflorum are somewhat wider and often have a more pronounced petiole. See Fig. 3.
| H. albiflorum | H. horridum |
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Photo by Don Rideout; see also pix of inflorescence | 
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| Fig. 3. Basal leaves of Hieracium albiflorum (left) and Hieracium horridum (right). The photographs are arranged with showing plants with the fewest rosette leaves at the top of each column.
Click on the pictures for larger versions. | |
All photographs by Tom Chester except for the one credited to Don Rideout.