Northwestern Los Angeles County to western Riverside County, and coastal San Diego County in California, to San Quintin in northwestern Baja California, Mexico . Fewer than 30 populations are known to exist in the U.S. and nearly 60 percent are concentrated in three locations in southern California: Otay Mesa in southern San Diego County, along the San Jacinto River, and in Hemet, Riverside County .
Within the MSPA it is known from MU3 (Otay Mesa), MU4 (MCAS Miramar), MU5 (Ramona), MU6 (San Marcos), MU7 (Del Mar), and MU8 (Marine Corps Base Camp Pendleton) .
Vernal pools in San Diego, in man-made depressions and ditches that have the same hydrological dynamics as vernal pools; alkali playa habitat elsewhere in range (Riverside County) .
Polemoniaceae (Phlox family) . First described by Reid Moran in 1977 based on collection made in 1969 in northwestern Baja California, Mexico . The similar Navarretia prostrata can occur in similar habitats but is distinguished by flower and calyx differences, and pollen grain surfaces. Chromosomes: 2n=18 .
Low, spreading or ascending, annual herb 4-6 inches tall . The lower portions of stems are mostly hairless (glabrous), leaves are 1 to 5 cm long and finely divided into linear segments and slender spine-tipped lobes .
Blooms April- June when vernal pools are devoid of standing water . The small flowers are white to pale lavender with linear petals, and borne in small, flat-topped, leafy clusters .
Germinates from seeds left in the seed bank, produces fruit, dries out, and senesces in the hot, dry summer months . The fruit is an ovoid, two-chambered capsule covered by a viscous layer that becomes sticky when moistened . The seed can stick to an animal or bird visiting the vernal pool . There is evidence that there is a low pollen to ovule ratio suggesting frequent self-pollination however, it is not considered an obligate self-pollinator because this species can also outcross to other plants . Hypothetically, insects would be the main pollinators of the flowers . The Hymenopteran insect Perdita navarretiae (a type of mining bee in the Andrenidae family) has been documented to make repeated visits to N. fossalis, possibly for pollination.
Threatened by loss of habitat through development, urbanization, habitat fragmentation, grazing, agriculture, watershed alteration (drainage pattern), and invasive nonnative plants . Detrimental edge effects including recreational activities, foot traffic, and off-road vehicles.
As an obligate wetland species, Navarretia fossalis depends on compatible, seasonal inundation and is vulnerable to changes in water levels and periods of inundation . Abundance varies year to year depending on precipitation and the inundation/drying time of the vernal pool. This makes it difficult to obtain an accurate count of the number of individuals in a population because the ratio of standing plants to remaining seeds in the seed bank that makes up the population cannot be visually measured. Modifications to the uplands surrounding a vernal pool can negatively affect the pool’s hydrology, even if such modifications occur outside the pool’s surface watershed. Disturbance may also allow invasive plants or non-vernal pool species to occupy the pools and compete with vernal pool plant species and may also alter the composition of native species of a vernal pool .