San Diego Fiesta Flower

San Diego fiesta flower (Pholistoma racemosum) is one of three related plants with weak, sprawling stems and small white flowers that like shady areas and are often found along the trails, climbing through the shrubs of the sage scrub, using their branches for support. The others are white fiesta flower (P. membranaceum) and common Eucrypta (Eucrypta chrysanthemifolia). All have small white flowers that play peek-a-boo from gaps in the surrounding foliage. To add to the confusion, the two fiesta flowers share common names.

Description ^2,4,59

San Diego fiesta flower is a sprawling annual herb, often leaning on adjacent vegetation for support, reaching two feet in height on weak, brittle, many-branched stems. Leaves are opposite or alternate along the stems, on narrow-winged petioles that partially clasp the stem. Leaf blades are ovate to triangular, 1-3 inches long (2.5-8.0 cm) and nearly as broad; they are pinnately divided into 3-9 lobes that may themselves have a few broad, shallow secondary lobes. Upper leaves are gradually reduced in size often to three lobes. Both stems and leaves have hairs and sharp, recurved prickles.

Flowers are solitary or a few in loose clusters, blooming sequentially from the top. They are bisexual, radial and five-parted, less than 1/4 inch (0.5 cm) across. The bristly sepals are fused into a five-lobed calyx. Small leafy appendages, folds in the calyx, occur between calyx lobes.

The five-lobed corolla is usually white. There is a single globose ovary with a small, two branched style. The ovary is surrounded by a pale green nectary disc. The five stamens do not extend beyond the corolla. Flowers bloom from Feb.to May.⁴⁶⁸

The fruit is a dry, globose capsule, dark purple partially surrounded by the prickly calyx. When dry, the capsule splits open by two valves to release a few tiny, ovoid brown seeds that are strongly honeycombed.

Classification ^2,59  

San Diego fiesta flower is a dicot angiosperm, currently placed in the waterleaf family (Hydrophyllaceae).

Many years ago, species of Pholistoma were placed in the waterleaf family based on similar morphological characteristics. More recently, the availability of molecular data led to several reinterpretations of these plants including the merging of the waterleaf family into the borage family (Boraginaceae). In 2016, the Boraginales Working Group re-evaluated the borage complex and again recommended a separate waterleaf family.⁴²² Many botanists have accepted this revision and Pholistoma is found listed in the Hydrophyllaceae in both the oldest and most recent literature. Research into the relationships between the two families is continuing and the systematics is still evolving.

The genus Pholistoma is a small genus with just three species. All three occur in the Reserve; the other two are fiesta flower, P. auritum and white fiesta flower, P. membranaceum.

Ecology

We have found no literature reports of ecological adaptations of San Diego fiesta flower. However, it seems reasonable to assume that the strong, downward-directed prickles on stems and leaves provide the same clinging-climbing ability as do those of the related fiesta flower (P. auritum). Since the plant lacks methods for twining or adhering, these prickles allow it to gain purchase on neighboring structures and grow into the less shaded layers above.⁴⁶⁸

Human Uses

We have found no reports of uses either in the past or the present.

Interesting Facts ⁵⁹

The specific scientific name, racemosum, refers to the structure of the flower cluster and is derived from the Latin word “racemulus” which means the stalk of a bunch of grapes.