(DC.) Greene, 1897
Holocarpha macradenia, commonly known as the Santa Cruz tarweed, is an endangered plant endemic to Northern California.  Alternative common names for this plant are Santa Cruz tarplant, gumwood, gum plant, and rosinwood.
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 tarweed (Holocarpha macradenia) 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.
The growth habit of Holocarpha macradenia, the Santa Cruz tarweed, is on a single erect stem, with a few short branches starting halfway from the base. 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.
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 tarweed 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
Holocarpha macradenia, Santa Cruz tarweed, had been considered almost extinct by the year 1960. Subsequently it was listed as a California protected species and federal endangered species.   Colonies are found in the city of Santa Cruz in the Arana Gulch, Twin Lakes, and Graham Hill Road areas;  in the city of Watsonville in the Harkins Slough, Spring Hills Gold Course, and Watsonville Airport environs;  and the Elkhorn Slough and Porter Ranch in Monterey County. 
In the 1980s other colonies were found in the San Francisco Bay Area, including a colony in Pinole of western Contra Costa County. Ex-situ conservation of the colony was used to allow construction of a new shopping center, and all the plants were moved immediately across and east of Interstate 80 onto the CalTrans right-of-way.  In another successful experiment, Santa Cruz tarweed was shown to thrive when non-native grasses were removed in the Arana Gulch colony in Santa Cruz.
- 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)
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