Jepson Upgrade Key #2
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Jepson Upgrade Key #2: An Unknown Composite Shrub

Boneseed, a South African evergreen shrub that is naturalized in the hills of coastal sage scrub adjacent to Palomar College in San Diego County, California. This shrub has become a serious naturalized weed in Australia, forming massive thickets in all southern Australian states. It has also become an invasive weed in New Zealand.

The flowers of boneseed are unusual among sunflowers because the ray flower ovaries develop into an enlarged berrylike fruit, each containing a very hard, bony seed. Up to 2500 seeds per square meter have been recorded beneath established boneseed colonies. The seeds are commonly spread by birds and animals that eat the fleshy fruit. They digest the fruit, but the hard seed passes unharmed through their digestive system. Harvester ants have been observed carrying the fruits to their nests where they eat the flesh and discard the seeds. Brush fires may also stimulate seed germination by fracturing (splitting) the resistant seed coat along sutures, thereby allowing the seeds to imbibe water. Fruits and seeds are also carried in moving water.

Boneseed and the closely-related bitou bush were imported into Australia as ornamentals in the 1850s. They may have also been introduced unintentionally in a ballast dump from a South African ship. Boneseed and bitou bush are now two of Australia's most widespread and damaging environmental weeds. Several insect species have been introduced for biological control, including the soft shoot tip moth (Comostolopis germana) and boneseed beetles of the genus Chrysolina. Chrysolina beetles, including (C. quadrigemina) have been used successfully on Klamath weed (Hypericum perforatum) infestations in California.

Originally planted on the Palomar College campus about 20-25 years ago, boneseed has become naturalized in the nearby hills of coastal sage scrub; however, it appears to grow best during years with average to above average winter rains. During successive dry years it seems to prefer areas with more soil moisture, such as ravines at the base of the Palomar College Arboreteum.

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