There is no absolute definition for "houseplant." If it survives indoors, it is a houseplant. The more traditional houseplants are more popular because they are simply more adaptable to interior cultural conditions. However, my colleague Brent Green and I grew a redwood, Monterey cypress, blue gum eucalyptus, southern magnolia, several camellias, a sweetgum and a stolen bougainvillea in our dorm room at Cal Poly­San Luis Obispo.

Houseplants must be tolerant of dry interior air, confinement to containers and minimal light. The sunniest of homes is not as sunny as exposed areas of the garden. The largest of pots lacks the soil volume of the garden. Even a bathroom that may get steamy and more humid than the garden is relatively arid during most of the day.

Many of the best houseplants are originally from tropical regions, so are collectively known as "tropicals." Many were understory species, so don't mind shade much. Although they would prefer humidity, they don't seem to miss it much if not exposed to drying breeze. Because most have coexisted with many other voracious and greedy tropical species, confinement to containers is not a problem.

Houseplants that can be grown outdoors may have problems if relocated too rapidly from the interior to the garden, if they have adapted to the interior. It is sometimes best to do it quickly and get it over with, allowing foliage to become damaged and replaced with foliage adapted to the new environment. Otherwise, such plants must be slowly introduced to the environment and eventually planted during mild weather.

I couldn't help but laugh when one of my sixth-grade classmates recently told me that he, too, had preserved his "leaf types" display from Camp Redwood Glen in 1978. Everyone in our class made one, with samples of three leaves that demonstrated each of the three types of veining: pinnate, palmate and parallel. Although the counselor did his best at the time to answer my incessant foliar questions, I had no idea the leaves were from Eucalyptus globulus, Hedera helix and Phormium tenax; or that I would eventually need to learn countless other leaf types.

Although most prone to desiccation among houseplants, one of my favorite leaf types is bipinnately compound, because it sounds so impressive and interesting. Veins of a pinnate leaf radiate from a central "midrib," unlike veins of palmate leaf, which radiate from the petiole (leaf stem) union. Compound leaves are divided into smaller leaflets. Therefore, bipinnately compound leaves are composed of small pinnate leaflets pinnately arranged on pinnately arranged leaflets.

Flower of the Week:
Yellow Bird of Paradise

Bipinnately compound foliage is what creates the very finely textured appearance of many leguminous species (within the family Leguminosae), including silk tree, jacaranda, mimosa and poinciana. Although these species are popular primarily because of their colorful bloom, the foliage alone is appealing.

Yellow bird of paradise, Caesalpinia gilliesii, is perhaps one of the more popular poincianas, but is still quite rare. It prefers soil that drains more efficiently than the dense clay soil endemic to the Santa Clara Valley, and it may defoliate during cooler winters. Specimens that are protected from frost may be evergreen, but will not bloom as colorfully as those that are more exposed to heat and cold. In fact, if soil drains well and irrigation is generous but infrequent, yellow bird of paradise may be happy in locations that are too hot for other species.

Hummingbirds enjoy the bright flowers, which have very prominent red stamens and diminutive yellow petals.

Horticulturist Tony Tomeo can be contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.