The Xerophytic Rose

Plants of the rare, drought-tolerant Rosa minutifolia are sometimes offered to visitors at sales in the Quail Botanical Gardens, Encinitas, California.

The native stand of Rosa minutifolia in California is confined to a single quarter-acre plot in the southwest corner of San Diego County. There are more in Baja California, on a strip near the coast extending from Ensenada south to El Rosario. All are under maritime influence with mild summers and nearly frost-free winters.

As is typical in Mediterranean climates, rain­fall occurs in fall and winter months, generally from November through March. Even during this period precipitation can be sparse, usually ten inches or less. Rosa minutifolia is, therefore, xerophytic, and in this respect is a typical member of the coastal sage scrub. Leafless in summer, it easily survives as long as nine months without water. When the rains come, it responds rapidly with growth, flowering, and setting of seed. This winter-spring pattern of growth and bloom is possible because of the virtual absence of frost.

The Baja California plants of Rosa minutifolia were discovered in 1882 by Dr C C Parry, but the small California stand was discovered only in 1985 by botanist Jack Reveal. Parry recognized it as a new and distinct species and sent herbarium material to Dr Engelmann in St Louis, who wrote: “A most striking and lovely species, distinguished from all other roses by its minute, deeply incised leaflets.”

The small stand of Rosa minutifolia in San Diego County is on west Otay Mesa, east of Imperial Beach, about six miles from the coast. Last March it was a fine sight, with many slender new canes clothed with tiny, bright green leaves and a profusion of tiny pink flowers. (A white-flowered variety is found only in Baja California.) Although the individual flowers are virtually without scent, the air was permeated with a light pleasing fragrance.

Rosa minutifolia is little known outside California. It is found in some botanical gardens and a few private gardens. The oldest planting is probably in Rancho Santa Ana Botanical Gardens, where former director Lee Lenz has observed it for over twenty years. His three plants never produced seeds, so he concluded that they probably were one clone, grown from cuttings. This rose is known to be self-infertile, but seeds are produced readily in mixed stands.

Propagation methods include seeds (no stratification is needed), cuttings, division, and layering. Tissue culture has not been successful to date. To my knowledge, no hybrids have yet been produced. As with most southern rose species, it is a diploid, so it would not hybridize with modern tetraploid cultivars.

The distinctive characteristics described by Engelmann, along with the bast fibers in the tissue (known in only two other rose species), led to placement of this rose in a new subgenus of Rosa: Hesperhodos. It was the sole species in this subgenus until the discovery in New Mexico in 1893 of Rosa stellata, whose strong affinity with R. minutifolia (including bast fibers in the tissue), small leaves, and drought resistance indicate a possible common ancestor.

Preservation of the small stand of Rosa minutifolia in California is a concern of Quail Botanical Gardens. The rose was recently placed on the California Endangered Species list, and we hope to preserve it in place, as well as to distribute propagating materials to botanical gardens throughout the world.

The Botanist’s Rose

Engelmann’s description of Rosa minutifolia is typical of the care required to distinguish plants that are superficially similar. This rose is described as follows:

A much branched shrub, two to four feet high, shoots pubescent, densely covered with straight or slightly recurved red-brown spines. The leaves have broad, divaricately auriculed stipules and mostly five leaflets. Fertile branches bear numerous terete subulate spines, some of the more persistent ones often in pairs under the branchlets. Leaves fasciculated on short spurs, narrow stipules divaricately auricled. Leaflet minute (only one to two lines [one-twelfth to one-sixth inch] long, the lowest pairs the smallest), oval, simply incised dentate, pubescent, not glandular. Flowers single, three-quarters to one inch wide on tomentose, bractless peduncles from between the leaves. Calyx-tube globular, densely setose-hispid, a thick nectariferous ring contracting its opening. Petals suboricular, scarcely emarginate, deep rose-purple or white. Central ovules borne on short stipes; styles distinct, short, woolly.