Greene

Caper Family Capparidaceae

Blackbrush

Torr. Rosaceae

Its dark gray bark makes this intricately branched shrub appear black from a distance, creating a rather somber landscape. When it blooms in April and May, however, blackbrush is quite pretty. There are no petals; the four sepals, all bright yellow on the inside, take over the function of petals, attracting pollinators to the cluster of stamens and pistil in the flower's center. The tiny leaves are gray and arise in pairs on the spine-tipped branches.

Blackbrush is not widely distributed, but where it occurs it is often dominant. It is found in a narrow band from southeastern California across southern Nevada and northern Arizona into southern Utah. The plants tend to grow where rainfall is rather high—from ten to twenty inches a year. For many desert shrubs, this is simply too much rain, but not for blackbrush, which thereby gains dominance over a large territory.

The seeds germinate only when spring rains are unusually early. Even when this uncommon event happens, most seedlings fail to survive past their first year. The result is a community in which individuals only rarely become established. But, because the shrubs grow slowly and live to a great age (well over one hundred years), the seedlings that do survive maintain their position for a long time, making it difficult for new plants to find space.

Brittlebush

At its best, brittlebush is a hemisphere of blue-green leaves; at its worst, it is a collection of white stems to which a few withered, gray leaves cling like bedraggled flags. The plants alternate between these two personalities on a seasonal basis. After winter rains moisten the soil, an entire canopy of new leaves replaces the old. Taking advantage of sunny days and damp soil, these leaves manufacture sugars at a rapid rate.

As the soil dries out, most leaves fall. The few that remain are small and covered with hairs pressed flat against the leaf surface. They manufacture sugars, too, but at a much lower rate, since the dense coat of hairs reflects much of the incoming sunlight. This is not a disadvantage, however; deflecting solar radiation keeps the leaves from becoming too hot and also retards water loss. These white or gray leaves cling to the stems for many months unless the soil becomes extremely dry, whereupon they also fall. Because drought induces dormancy in the stem tip, no new leaves can be produced until rains have moistened the soil once again. Then the cycle begins anew.

When brittlebush blooms in the spring, entire hillsides turn yellow. The blossoms are large for a desert plant, about the size of a half-dollar. Each contains numerous disk flowers in the central medallion and about a dozen ray flowers on the perimeter. Across most of the desert, both types of flowers are yellow, but along the lower Colorado River, the disk flowers are often dark purple. Brittlebush is found from southern California and southern Arizona into the adjacent Mexican states of Baja California and Sonora. Butterflies, moths, and small beetles pollinate the flowers.

Green brittlebush

(A. Gray) A. Gray Compositae

This rounded shrub about two or three feet tall is notable for its brittle, white stems and rough, dark green leaves. Green brittlebush puts out its bright yellow, bell-shaped flower heads whenever rainfall provides the opportunity. The plants are opportunists in other ways, too. Unlike brittlebush, its grayer relative, the leaves of green brittlebush lack a dense coat of hairs. They cannot adjust their photosynthetic pace to suit the climate. When soil moisture is high, the plants produce abundant new leaves, which photosynthesize at a rapid rate, producing the sugars needed for growth. As the soil dries out. the leaves drop and the plants become dormant until the next rainfall.

Green brittlebush colonizes disturbed spots such as roadsides and washes. Although plants growing in washes are liable to be ripped out by flash floods and those at roadsides may be mowed or sprayed or trampled, green brittlebush has little choice in its habitat. Because the plants have no mechanisms to prevent excessive water loss from their leaves, they need plenty of moisture, which they get from rainfall and runoff from roadsides and washes.

The species occurs from southeastern California to eastern Arizona and north into southern Nevada and Utah.

Cooper golden bush

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