Haworthia is a genus of more than 60 species of succulent herbs from southern Africa that are named for the 19th century British botanist Adrian Hardy Haworth. One of the distinctive characteristics of the plant genus is that the leaves form rosettes, which are sometimes rectangular instead of circular, as they grow. These plants are sometimes listed as belonging to the Liliaceae, or lily, family and other times listed as the Asphodelaceae family. The lily family was a large family that was divided into smaller groups; Asphodelaceae is one of the newer families. Some older references for some of the haworthia plants include Liliaceae in the name.
The haworthia plants, sometimes called the star cactus or wart plant, generally have thick leaves, as do most succulents. Generally, the leaves may have white, cream, or red tubercle or nodules, spots, veins, or edges. The leaves also may be variegated in any combination of greens, white or cream, yellow, or shades of red. Leaves may be sharply pointed or stubby and flat-topped, depending upon the species. A few grass-like haworthia plants have long, thin leaves.
Growers sometimes call it the "window plant" because the leaves often have translucent areas. To survive strong sunlight, wild haworthia plants usually are submerged in sand or sandy soil with only the translucent tips of the leaves above the ground. The plant grows a flower stalk that has inconspicuous flowers, which usually are lily-like. Flowers may be white, green, rose-striped, or pale lavender.
One of the haworthia plants that gardeners often raise is the zebra plant. This actually refers to two plants: Asphodelaceae h. attenuata and Liliaceae h. fasciata. Its dark-green leaves have white-raised beads that connect to form bands or stripes. The leaves grow in an upright, slender rosette of leaves that taper inward. Like many of the plants, gardeners generally raise the zebra plant outdoors in warmer climates and indoors as a houseplant in colder climates.
Many different haworthia species have a variety of leaf characteristics. One of these is the popular plant is H. cymbiformis, which has thick, light-green leaves that are transparent at the tips. The flat-topped, stubby leaves of H. truncata make it a popular houseplant and garden specimen where the climate allows. In contrast, the H. blackburniae has long, thin leaves.
Haworthia plants generally need sandy soil, warmth, proper moisture, and ample sunlight. Mealy bugs and fungus gnats may attack them when grown as houseplants. If a gardener sees fungus gnats, he or she should reduce the watering schedule and treat the soil with an insecticide suggested by a horticulturalist. Sometimes covering the soil with pea-sized gravel will help deter the gnats. Gardeners typically fight mealy bugs with systemic insecticides.