| Holocarpha macradenia | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Asterids |
| Order: | Asterales |
| Family: | Asteraceae |
| Genus: | Holocarpha |
| Species: | H. macradenia (DC.) Greene, 1897 |
| Binomial name | |
| Holocarpha macradenia |
|
The Santa Cruz Tarweed is an endangered plant endemic to certain coastal terraces in Northern California. Its principal range is in Santa Cruz County and Monterey County, but smaller colonies have been found slightly to the north. Specifically Santa Cruz Tarweed (Holocarpha macradenia) likes to inhabit terraced locations of valley or prairie grasslands with underlying sandy clay soils. Its characteristic habitat, the California coastal prairie ecosystem, may be the oldest stable ecosystem of the temperate world, dating about 600,000 years. The growth habit is on a single erect stem, with a few short branches starting halfway from the base. It has characteristic yellow daisy-like flowers, with black anthers giving the appearance of striking black dots in the flower center. This plant is sometimes known as the Santa Cruz Tarplant.
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Santa Cruz Tarweed is distinguished from other members of its genus by possessing eight to sixteen three-lobed outer ray flowers and 40 to 90 central disk flowers, more than any of the related species. The flowers are situated in dense clusters at the branch tips or along the branch on a very short stem. Its leaves are linear and manifest longer near the plant base. The lower ranging leaves exhibit sharp, short teeth at their edges, while the upper leaves present edges that are rolled back, leading to a bristly feeling. The aroma of the plant has variously been described as strong, citrusy, tangerine and Christmas Tree like. Alternative common names for this plant are Santa Cruz Tarplant, gumwood, gum plant and rosinwood. In any case the pungent smell protects it by repelling many would be feeders.
The Santa Cruz Tarweed has an extremely long tap root allowing it to thrive longer into the season beyond most coastal wildflowers. The plant produces seedbanks, which may not germinate in the next season, but which can remain viable over a period of years. Blooming season is summer when there is less competition for pollinators and also less competition for sunlight, since in its range many plants have died back from the summer drought. Further protection from the rainless summer is a resiny coating on leaves and stems, allowing retention of water until late in the season. These resins often adhere to livestock, and, in the case of facial adherence, lead to a mascara effect after dust is further added.
The Santa Cruz Tarweed had been considered almost extinct by the year 1960. Subsequently it was listed as a California protected species. Colonies are found in the city of Santa Cruz (Arana Gulch, Twin Lakes, and Graham Hill Road areas); in the city of Watsonville (Harkins Slough, Spring Hills Gold Course and Watsonville Airport environs); and on the Porter Ranch in Monterey County. It has also been found in the Elkhorn Slough area. In the 1980s other colonies were found including locations as far north as western Contra Costa County immediately east of I-80 by Earth Metrics Inc. In a successful experiment, Santa Cruz Tarweed was shown to thrive when non-native grasses were removed in the Arana Gulch.