|The Santa Cruz tarplant is listed as threatened under the federal Endangered Species Act (ESA), and endangered under the state of California Endangered Species Act (CESA).|
(DC.) Greene, 1897
Hemizonia macradenia DC. 1836
Holocarpha macradenia, commonly known as the Santa Cruz tarplant, is an endangered plant endemic to Northern California.  Alternative common names for this plant are Santa Cruz tarweed or Santa Cruz sunflower.
The plant's principal range is on certain coastal terraces in Santa Cruz County and Monterey County. Smaller colonies are to the north in Alameda County, Contra Costa County, and Marin County. It is found from sea level to 110 metres (360 ft).
Specifically Santa Cruz tarplant likes to inhabit terraced locations of coastal or valley prairie grasslands with underlying sandy clay soils. Its characteristic habitat is in the California coastal prairie ecosystem, which may be the oldest stable ecosystem of the temperate world dating from about 600,000 years ago.
Santa Cruz tarplant is an annual wildflower that can grow to 50 cm tall, but is often much smaller. The flowering period is June to November. The growth habit is a single erect stem with larger specimens developing branches. 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. Several other species have a similar general appearance, and can be easily mistaken for the Santa Cruz tarplant. The real Santa Cruz tarplant, though, has distinctive glands (see photos) that are not present in lookalikes.
It has characteristic yellow daisy-like flowers, with black anthers giving the appearance of striking black dots in the flower center. It is distinguished by its large number of flowers: 8 to 16 three-lobed outer ray flowers and 40 to 90 central disk flowers, more than any others in the Holocarpha genus. The flowers are situated in dense clusters at the branch tips or along the branch on a very short stem.
- Drought tolerance
The Santa Cruz tarplant has an extremely long tap root, allowing it to thrive longer into the season than 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 resinous 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-like effect after dust adheres to the resin in turn.
Protection and current status
Santa Cruz tarplant had been considered almost extinct by the year 1960. Subsequently it was listed as a California endangered species and federal threatened species.   Colonies are found in the city of Santa Cruz at the Arana Gulch greenbelt and near De La Veaga Golf Course, Twin Lakes, and along Graham Hill Road;  in the city of Watsonville in grasslands along Harkins Slough, Spring Hills Golf Course, and on Watsonville Airport property;  and in the Elkhorn Slough watershed at the Elkhorn Slough Foundation's Porter Ranch in Monterey County. 
In the 1980s other colonies were found in the San Francisco Bay Area, including a colony in Pinole, western Contra Costa County. Ex-situ conservation of that colony was used to allow construction of a new shopping center, and a limited number of seeds from that population were moved immediately across and east of Interstate 80 onto the CalTrans right-of-way.  Additional seeds from that population were moved onto East Bay Regional Parks property, where most of these introduced populations died. In another touch-and-go experiment, Santa Cruz tarplant has been shown to barely hang on at the Arana Gulch colony in Santa Cruz, mostly do to lack of appropriate management, habitat fragmentation, and competition with non-native species.
- The Plant List, Holocarpha macradenia (DC.) Greene
- CalFlora . accessed 11.14.2011.
- Jepson . accessed 11.14.2013
- USDA: Legal status . accessed 11.14.2011.
- Santa Cruz County, California: Local Coastal Program Land Use Plan (1981)
- Gary Deghi, C. Michael Hogan et al., Environmental Impact Report, Harkins Slough Area for the City of Watsonville, Earth Metrics Incorporated (1985)
- PelicanNetwork.net; article by Jane Strong, (2000).
- Gary Deghi, C. Michael Hogan et al., Final Environmental Impact Report of the Pinole Valley Shopping Center for the city of Pinole, Earth Metrics Incorporated (1986)
|Wikimedia Commons has media related to Holocarpha macradenia.|