Dudleya brevifolia

While the majority of species of Dudleya tend to have woody, above-ground stems, in this species the stem has been reduced to a subterranean, corm-like structure. This corm is elongate, and measures 1.5–3.5 cm (0.59–1.38 in) long by 1–6 mm (0.039–0.236 in). Emerging from the corm are the rosettes of basal leaves, with usually one rosette of leaves per plant, but sometimes increasing to up to 3. The rosettes measure 0.5–4 cm (0.20–1.57 in) wide. There are 5 to 15 basal leaves, more or less spheric to spoon-shaped distally, which are usually buried in the soil except for the top surface of each leaf blade. The leaves measure 0.7–1.5 cm (0.28–0.59 in) long by 2–7 mm (0.079–0.276 in) wide and 2–4 mm (0.079–0.157 in) thick. The leaves have a long, narrow petiole connecting them to the stem.[1][7]

The peduncle is 2–11 cm (0.79–4.33 in) tall by 0.5–1 mm (0.020–0.039 in). The peduncle is covered in 10 to 20 bracts. The bracts are shaped triangular-ovate to sub-orbiculate (nearly circular) or reniform (kidney-shaped). The bracts measure 0.2–1 cm (0.079–0.394 in) long by 2.5–8 mm (0.098–0.315 in) wide and 2–6 mm (0.079–0.236 in) thick, with the tip of bracts obtuse. The lower bracts are less than 1.5 × longer than they are wide. The terminal branches (cincinni) on the inflorescence, of which there are typically very few, measure 1–4 cm (0.39–1.57 in) long and have 3 to 10 flowers.[1][7]

The flowers are white and star-shaped, with a yellow center. The petals are connate 0.7 mm (0.028 in), and spread from near the middle. They are white, colored pinkish on the keel, turning yellow towards the center, and are also often lined with red. The shape of the petals is elliptic, and they measure 5–8.5 mm (0.20–0.33 in) long by 2–3.5 mm (0.079–0.138 in) wide, with the apex subobtuse. The entire corolla measures 8–15 mm (0.31–0.59 in) in diameter. The flowers tend to have a musky-sweet odor.[7]

The plant was first collected by F. W. Peirson at Torrey Pines in 1922. Willis L. Jepson, in line with the common scientific view at the time, regarded the plant as a new species of Sedum. Specimens later discovered in the area were unable to be distinguished from Hasseanthus blochmaniae (Blochman's dudleya).[4]

The genus Hasseanthus, now moved into a subgenus of Dudleya, includes plants characterized by a geophytic habit. A 1950 treatment of the plant by Reid Moran would then place it under the subspecies brevifolia of H. blochmaniae, noting some significant morphological differences. The genus Hasseanthus would later become a subgenera of Dudleya.[4]

By 1975, Moran's assessment of the species in the journal Baileya was more grim. Lamenting the "progress of civilization," he reconsidered it as a species in its own right, noting that the destruction of the introgressive populations that graded into Blochman's dudleya made these plants distinct enough to be deemed a species.[5]

With lichen, moss, and ironstone concretions, overlooking the Carmel Valley.

Two species of deciduous Dudleya graded into the population of Dudleya brevifolia. Hybrids with Dudleya edulis have also been reported.[7]

One population approached Dudleya blochmaniae at a mesa east of La Jolla. The plants flowered three to four weeks earlier than the other populations of D. brevifolia, and had a different growth habit, being primarily found in depressions on the mesa. Compared to brevifolia, their rosettes and cauline leaves were slightly longer and narrower. The basal leaves and corms approached brevifolia.[9] Moran noted how it was difficult to distinguish brevifolia from blochmaniae until the advent of land development in the area extirpated the populations that transitioned between the two.[4][5]

The plant was also known to grade into Dudleya variegata abundantly at a vernal pool-like depression north of Eastgate Mall road and west of the I-805 near Miramar and the Sorrento Valley.[10][11][3] The location is now an office park.[12] The hybrids possessed intermediate traits.[11][13]

As this plant is a geophyte, occupying a habitat consisting mostly of hardpan substrata, it has an unusual growth habit in which once the tuberous, underground stems hit the hardpan, they will then spread out horizontally along the surface of the impenetrable substrate. In areas with the most shallow soil that is still conducive to growth, this plant tends to have incredibly irregular stems.[17]

Annual growth begins after the first autumn rains, but this can be disturbed by any mid-winter drought conditions. If the plants are disturbed by any winter droughts, they will return back to dormancy and wait until the next suitable growing season. This is most common in smaller plants, whilst larger plants will usually retain their leaves even through mid-winter droughts. This response may be mistaken for the death of plants, which are in fact dormant underground.[17]

Timing of rains may be more important than the quantity. Years with consistent and evenly spaced autumn-winter rains correlate with the most flowering individuals. Likewise, lack of precipitation in the middle of winter is associated with less plants flowering. In any given year, 10% to 30% of individuals will flower. This means that population estimates made from flowering plants may significantly undercount the number of individuals.[17]

• Phenology of Dudleya brevifolia
• 
  Plants emerge after winter rain.
• 
  Nascent inflorescences start.
• 
  Basal leaves fully disappear, buds nearly mature.
• 
  Flowers begin to open.
• 
  Plant flowers and fruits, before going dormant for the rest of the year.

This plant may reproduce through seed or via vegetative means. The vast majority of Dudleya species have difficulty in rooting from detached leaves, a trait that distinguished them from Echeveria in early taxonomic studies. In most rosette-forming evergreen Dudleya, the leaves will simply callous, wrinkle, and die.[18] However, some species, especially deciduous ones, may reproduce readily from detached leaves. One to three weeks after the leaves are detached from the plant, roots will emerge from the petiole base.[17]

Flowering at the edge of a mesa.

Seeds are typically dispersed by wind or water. The seeds are small, but are larger in comparison to other members of Dudleya, as plant size is inversely correlated with seed size.[19] The dried inflorescences may detach and tumble along the sandy mesas, which presumably may disperse seed.[17]

Many pollinators make visits to the flowers of D. brevifolia. These include bee flies (Bombyliidae), hover flies, soft-winged flower beetles (Dasytes species, within the family Melyridae), western honey bees, bumble bees and digger bees (tribe Anthrophorini).[17]

Dudleya brevifolia is currently listed as an endangered species by the state of California and by the California Native Plant Society.[14][8]

Dudleya blochmaniae subsp. brevifolia was listed as an endangered species by the U.S. Fish and Wildlife Service in January 1982. In October 1996 they withdrew federal protection as an endangered species, citing the threats to the species had diminished and that it was a "covered species" within the Multiple Species Conservation Program (MSCP) of southern San Diego County.[23]