James Russell Lowell’s poem, “What is So Rare as a Day in June,” offers a lyrical perspective on nature, and suggests the rare (or perhaps just uncommon) plants that avid gardeners find appealing.

At the recent annual plant sale by Cabrillo College’s Horticulture Department, I picked up two that qualify as uncommon.

One is a crested iris, Iris gracilipes, the slender woodland iris from China and Japan, which is where most crested iris species grow.

The crested iris gets its name from a yellow or white crest (like the beard on a bearded iris) along the sepals (like petals). Typically, they are dwarfs, growing about eight inches tall, with violet blossoms about one or two inches across. They prefer a shady, moist spot in soil that is slightly acid. Now I need to find such a place for it in my garden.

My other uncommon treasure from the sale is a Puya venusta, which is called “Chagualillo” in Chile. I already have P. berteroniana and P. coerulea, so I could claim to be a small-scale collector of these Chilean plants. The puyas are bromeliads (pineapple family members) with spectacular blossoms. P. berteroniana, for example, has “6- to 10-foot flowering spikes of metallic, deep bluish-green flowers highlighted by vivid orange stamens.”

Who would —or another gardener—want to own a Japanese crested iris or a Chilean puya?

The obvious explanation might rest on the pleasure of dazzling garden visitors with plants they are unlikely to have seen elsewhere. In fact, one could see puyas at the Huntington Garden or the U.C. Berkeley Botanic Garden, but probably not at a garden center or most residential gardens.

Another, less vainglorious reason for growing uncommon plants is to enjoy them privately for their own sake, and to learn their cultivation.

A truly selfless motivation would be to conserve a plant genus or species that is in danger of extinction. According to California’s Department of Fish and Game (DFG), this state is home to over 6,500 species, subspecies, and varieties of native plants. Of these, 223 are designated under California law as rare, threatened, or endangered. The threat of a plant’s extinction is often based on human encroachment or destruction of the plant’s habitat.

In 1968, the California Native Plant Society began its Rare Plant Program in coordination with the DFG, to develop current and accurate information on “the distribution, ecology, and conservation status of California’s rare and endangered plants.” The CNPS generally wants such plants to thrive in their natural setting, but also endorses “conservation gardens,” as a substitute home for plants that lose their natural habitats to the relentless march of progress.

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The concept of a “rare” plant could be interpreted in different ways, depending on the interpreter. California’s Department of Fish and Game does not have an official definition for a “rare” plant. California’s Fish and Game Code, however, includes definitions of “endangered” and “threatened” species, as follows:

"Endangered species" means a native species or subspecies of
a bird, mammal, fish, amphibian, reptile, or plant which is in
serious danger of becoming extinct throughout all, or a significant
portion, of its range due to one or more causes, including loss of
habitat, change in habitat, overexploitation, predation, competition,
or disease.

"Threatened species" means a native species or subspecies of
a bird, mammal, fish, amphibian, reptile, or plant that, although not
presently threatened with extinction, is likely to become an
endangered species in the foreseeable future in the absence of the
special protection and management efforts required by this chapter.

The Fish & Game Code also defines a “candidate” species:

"Candidate species" means a native species or subspecies of a
bird, mammal, fish, amphibian, reptile, or plant that the commission
has formally noticed as being under review by the department for
addition to either the list of endangered species or the list of
threatened species, or a species for which the commission has
published a notice of proposed regulation to add the species to
either list.

Some commercial firms that sell plants will specialize in, or feature, plants that they call “rare.” Several such plant purveyors can be located by searching the Internet for “rare plants,” but whether their plants are actually rare in the sense of “not found in large numbers and consequently of interest or value,” is a matter of personal opinion.

These sellers may be expected to employ a relatively inclusive definition of rarity, to avoid a situation in which their livelihood depends on many customers seeking a very small number of plants.

If a plant meets your personal definition of rareness, you can enjoy it even if it could be found in great numbers somewhere else in the world.

Example: At the San Francisco Flower & Garden a few years ago, I bought an enormous bulb of the Giant White Squill, which I had never seen. The bulb was larger than any other bulb I had encountered (they can be as large as a soccer ball, and 8-to-10 pounds), and I had no idea what a Giant White Squill might be, so it certainly qualified as rare in my lexicon.

I soon learned that the Giant White Squill is Urginea martitima, a plant that is native to the Mediterranean Basin and fairly common as a roadside volunteer. No matter: it is still a rarity in my garden.

Snails relish the plant’s large fleshy strap-like leaves, so it has had a tough time in my garden, but I am still expecting to see a flower stalk in August. It could be six feet tall!