Big Saltbush

At first glance, big saltbush is a large, rounded, woody, grayish, dull bush with inconspicuous flower clusters and an uninspiring name, found in tough areas such as alkaline and saline washes, dry lakes and scrub.

Never-the-less, in spite of the inauspicious appearance, and mundane lifestyle, big saltbush has one surprising talent that is shared by very few other terrestrial plants: a single plant can change from a male to female and vice versa. This is providing a whole new twist on plant reproduction for evolutionary ecologists to ponder.

Description ^{4,11,23,24,67}

Big saltbush (or Brewer’s saltbush) is a large, evergreen shrub, usually less than 8 feet (22 meters) in height and often wider than tall. The shrubs are densely branched, making impenetrable thickets. The leaves are a silvery blue-grey, on short petioles, arrow-head or ovoid-triangular in shape, and are often wavy. Lower leaves are larger, up to about 2 inches (5 cm) long. Leaves and stems are densely covered with bladder hairs (vesicular hairs). These highly modified hairs excrete salt and give the leaf a silvery sheen when the leaf is young and a rough, scaly texture as the leaf ages.

Tiny flowers are inconspicuous and either male or female. One to several flowers are tightly clustered into small bead-like clusters (glomes), which are spaced along small spike-like branchlets. Male and female flowers may be on separate plants (dioecious) or on the same plant (monoecious) in which case they are usually in separate glomes with the glomes of male flowers above the female flowers. Plants may change sex, possibly in response to environmental conditions. ^5,67

Petals are lacking. The male flower has a five-lobed calyx that is yellowish or reddish. There are five stamens, each topped with a bi-lobed anther that releases yellow pollen. The female flower has no stamens and one ovary tightly enclosed by two small flattened-ovate bracts (technically called bracteoles) that resemble sepals and are fused along the lower margins. A whitish style divided into two linear branches protrudes from the surrounding bracteoles. As the single seed develops, these bracteoles take on the appearance of tiny clam shells and the glomes become congested along the branchlet.  The seed is a shiny brown, slightly wrinkled ovoid that is less than 0.1 inch (2mm) in maximum dimension.

Classification

Big saltbush is a dicot angiosperm that most references ^{2, 306} place in the goosefoot family (Chenopodiaceae),  although, based on molecular evidence, some systems consider it a subfamily in the amaranth family (Amaranthaceae).^{41, 143} Plants in this family are often succulent or scaly; many appear weedy; many are salt tolerant. Typical flowers are tiny, greenish and lack petals.^{11, 34, 44, 143} Well known members of the goosefoot family include beets, spinach, and quinoa.^11,44 In the Reserve, a common goosefoot is pickleweed (Salicornia pacifica).

Atriplex is a genus of about one hundred species,¹¹ forty-two of which are found in California.⁷  Species of Atriplex are distinguished from other members of the family by the structure of the female flower, which is enclosed in two bracts that are fused only at the base.¹¹

In the past, subspecies of A. lentiformis have been recognized. The coastal form, with larger leaves was called ssp, breweri, and this gave rise to the common name Brewer’s saltbush. A more recent interpretation ^{2, 306} is that the within species variability is due to environmental factors, rather than genetic differences and subspecies have been merged.

Ecology ⁵⁴⁵

Big saltbush, as its name implies, can withstand concentrations of salt that would defeat most land plants. Like many species in the goosefoot family, this is accomplished by possessing highly modified hairs on the surfaces of the young stems and leaves; these hairs serve a function similar to that of the bladder cells in pickleweed (Salicornia pacifica) or the salt glands on the leaves of saltgrass (Distichlis spicata).

The bladder hairs (or salt hairs or vesiculated hairs) consist of one or more stem cells, and a terminal bladder cell. Together they look like tiny balloons tethered to the leaf surface. Salts in water absorbed by the roots are moved out of the cell sap and into the bladder hairs, which can expand many times their original size, much like inflating balloons. The surface of young vegetation has a sheen from the tiny bladders. Once the bladders reach capacity, they collapse, releasing their salty contents onto the leaf surfaces to be blown or rinsed away. The bladder hairs do not regenerate, but the remnant fragments often accumulate, giving surfaces of older leaves a scurfy texture and rough feel.

Human Uses

The tiny seeds of big saltbush were eaten by native Californians as an ingredient of pinole, ^5,34,67,282 a staple used by native Americans throughout much of California, made from any of a variety of nut-like seeds of grasses and flowering annuals. ⁵⁴⁸ Seeds were ground into a fine flour (the pinole) which was eaten dry, or made into a mush or baked in a stonelined pit and reground into a meal which was moistened into a mush. ⁷⁵

Some tribes made the plant into a soap.^{15 34}  Kumeyaay ground the stems and leaves into a poultice for ant bites.¹⁶

Recently, big saltbush has become an important component of revegetation projects.⁵ It not only thrives in tough place, especially in areas with saline or alkaline water or soil  but provides erosion control and wildlife habitat, and the foliage has reduced flammability.

Interesting Facts

The typical plant has flowers that each contain male and female organs. A few plants (estimated  5-6%) ⁵³⁸  have female flowers on one pant and male flowers on different plants (dioecious); and even fewer plants have separate male and female flowers that occur on the same plant (monoecious).  In the context of species adaptability and survival each of these sexual systems has evolved in response to opposing selective pressures. Their roles in the context of plant evolution was first pondered by Darwin ⁵⁴⁵ and has engaged many botanists for many years since.

Darwin recognized that a spectrum of sexual systems exists. For instance, the lemonade berry (Rhus integrifolia) has some plants with bisexual flowers and others with female flowers, while the laurel sumac (Melosma laurina) has male flowers on some plants and predominantly (but not entirely) female flowers on other plants. Big saltbush is usually either all male or all female, but may have both genders on a single plant. In some plants, like big saltbush, these different expressions of gender seem to be driven by environmental variations such that the male and female plants are separated along some environmental gradient, with the female plants more frequent under more favorable conditions. This has been dubbed the Jack Sprat effect after the first report of a division of resources among the sexes.

To further complicate the question of sex in plants, some plants including species in the Atriplex genus, can change sex over time. ⁵⁴⁷ For instance, in one five-year study of seventy  A. lentiformis shrubs, 30% changed their gender expression one or more times, including going from male to female or female to male with or without passing through the intermediate stage.