Desert Vegetation, The Principal Attraction (continued)

Short-Lived Annuals

When normal or above normal winter rains keep the desert soil moist for months, and when no late cold spell and no persistent drying winds blight the lavish growth which ensues, then ephemeral (short-lived) annuals cover the desert with a gorgeous patchwork quilt of bloom. Beginning as early as mid-February with desert sandverbena and Mexican goldpoppy, the spreading patches of color reach a peak in late March and early April. Shreve lists more than 150 species of these winter ephemerals common in the Sonoran Desert.

Some of these plants, one must remember, are not adapted to true desert conditions, but they take advantage of the favorable combination of moisture and temperature which prevails only during a cool, wet winter. Thus they are able briefly to monopolize the soil and, by compressing their growing season into a few weeks, to mature their seeds before the desert summer turns on its heat.

During the hot, dry periods of the year, the tiny seeds of these plants lie mixed with the soil. They are ready, when suitable conditions return, to germinate and start a new generation. This may not come about for a number of years.

"In dry years," writes Dr. Fritz W. Went of the Missouri Botanical Garden, "the seeds of certain annual plants lie dormant. This is not remarkable; what is amazing is that they refuse to germinate even after a rain, unless the rainfall is at least half an inch. The mystery is explained by the fact that some seeds have water-soluble germination inhibitors in their coverings. Rainfall in sufficient quantities to support the potential seedlings dissolves the coverings—anything less leaves the seeds dormant to await adequate moisture." When winter rains are scant or lacking, the seeds do not germinate, and the spring flower display fails to materialize.

The winter ephemerals, however, are not the only set of short-lived annuals. Another group blooms in summer. Thus the annuals respond to the two seasons of possible rainfall, December through February and July through September.

For the native perennials, there are also the two seasons of growth. The lesser one is in early spring, following winter rains and the rising temperatures. The major one occurs during the summer rainy season. The entire ecology of the perennials is adjusted to the summer rainfall.

Among the more than 150 species of winter annuals that spread their colors across sloping bajadas and along washes, a few produce the major part of the spring flower show. Sometimes a single species covers a relatively large area with a vivid mass of blossoms of one color; again two or three species mix to produce a bright yet harmonious blending of brilliant hues. In other sections of desert a general mixture of ephemerals develops. These do not all blossom at the same time; hence the pattern of color changes from day to day as the flowers of each plant, under the pressing urge of warm, drying breezes, develop rapidly toward the seed stage. Adding to this glorious display of annuals, the less hurried spring-flowering perennials join the blossom parade at overlapping intervals.

The more conspicuous spring ephemerals that combine with or follow the goldpoppy and sandverbena in developing mass displays are the purple-flowered escobita owlclover; several species of blue to violet lupines; the ground-hugging nama, or purple roll-leaf; and the evening-primroses, or sundrops.

Properly belonging with the perennials, but noticeable only during its spring blossoming period, the desertlily is among the most attractive of the monument's wildflowers; it resembles an Easter lily. The bulbs once were important in the diet of Papago Indians and, because of their similarity to garlic, were named "ajo" by the early Spaniards. This plant, abundant in the region, has given its name to a town, a valley, and a range of mountains—all of which are prominent in the geography of the monument.

(Left) Widespread and easily recognized, desert baileya may be found in bloom during any month of the year. (Right) Desertlily is one of the attractive flowers of early spring.

Abundant along roadsides, the yellow-petaled desertgold, or desert-sunflower, blossoms from January to June and attracts moths and butterflies. The tackstems are not abundant, but they are noticeable because they grow in robust white, rose, or pale-yellow clumps that somewhat resemble long-stemmed dandelions. Easily confused with them is the desert-chicory. Several species of phacelia, or wild-heliotrope, add to the monument's flower show. These plants, with white to violet or purple flowers, are usually found under shrubs and bushes rather than on the open desert.

The flowers of the globemallows, whose colors are usually grenadine, apricot, or orange, also attract attention. Many of the species are perennial and hence may be found in blossom throughout much of the year. Some annual species are small and erect and have large blossoms. Often growing along roadsides, they create bright-colored patches in early spring. Several of the perennial globemallows are tall, coarse, and conspicuous when covered with flowers. Globemallows may be found in bloom during periods when other flowers are conspicuous by their absence, and they help to fill the flowerless gap after the winter ephemerals have faded and before the cactuses and summer perennials are ready to blossom.

According to Shreve, the fast-growing herbaceous plants which appear after the spotty summer rains begin are as abundant and ubiquitous as the winter ephemerals. The seedlings become noticeable about 3 days after the first heavy downpour and soon carpet gentle slopes where the soil surface has been bare for months. In the Arizona upland there are few years in which starting conditions are favorable before July 10. Grasses are more richly represented in summer than in winter, both in species and number of individuals. There are fewer species of summer ephemerals than of winter ephemerals, but their role in the desert ecology is just as important.

Few of the hot-weather ephemerals develop mass displays or furnish the attractive color combinations provided by the cool-weather annuals, but a sufficient number of them are usually present to provide bright spots for the visitor who is willing to brave the summer heat. One of the more noticeable representatives of the group is the caltrop, or summer-poppy, whose large blossom somewhat resembles that of the Mexican gold-poppy. Its local name is Arizona-poppy.

Even during the driest years, desert baileyas, or desertmarigolds, may be found, often near washes or along roadsides where pavement runoff provides additional moisture. The large yellow flower heads are readily recognized. Salt heliotrope, or quailplant, blooms throughout the year when moisture is adequate. Flowers are white to purple. Indians dried the roots and applied the powder to wounds and sores.

Spiderlings prefer open, sunny locations, where their trailing stems spread over the sandy soil. The purple flowers are small but grow in attractive clusters. Other common summer ephemerals, widespread but lacking noticeable flowers, include amaranth, or carelessweed, and spurge, of which there are many species. Pectis, or chinchweed, is another member of a big genus, a number of species of which are hot-weather annuals. Following summer rains, large areas may be covered with the small yellow flower heads of this strong-smelling plant. Indians are reported to have used it for seasoning foods.