By Charles Kidder
My niece was touring my garden and admired a variegated Osmanthus. A few feet beyond, we came upon another variegated plant, an Aucuba, and she proclaimed, “This must be related to that other one!” Well, not really.
Foliar characteristics don’t usually have much to do with plant relationships. Variegated plants are no more likely to be related than plants with plain green leaves. What really counts: the structure of the flower, as well as the actual DNA of the plants. The first is generally pretty easily observed in nature; the latter requires some kind of gizmo in a lab.
Plant geeks are fond of referring to plant families, a group of genera that are fairly closely related. There are six hundred-some families among all plants worldwide. While many are pretty obscure to lay people, some are quite familiar to most of us. Perhaps near the top of the list would be the Grass Family, the Poaceae, with over ten thousand domesticated and wild species.
Grasses may be best known to homeowners as lawns, but in the last few decades they are also commonly seen as ornamental plants in their own right. Miscanthus, muhly-grass, switch grass and blue fescue, to name a few, all provide a unique structure to the garden. But the biggest impact of grasses is in agriculture, rather than horticulture. Rice, wheat and maize provide half of all calories eaten by humans, making the grasses the most economically important plant family in modern times.
Another big hitter in the food department is the legumes, or the Leguminaceae. With 730 genera and 19,400 species, the legumes are most common in tropical rainforests and adjacent dry forests. We’re familiar with the beans, peas, chickpeas, soybeans and peanuts that make up a goodly portion of the human diet, while clover and alfalfa are important forage crops that we eat indirectly, perhaps even as honey.
The legumes are also showy and durable players in ornamental gardens. One of my favorites is Baptisia, with its white, blue or yellow flowers. Once established, this drought-tolerant perennial can assume shrub-like proportions in each growing season. The bush lespedezas are also perennials with shrub-like tendencies that get even larger, but can be whacked to the ground every year. One of the few woody legumes that grow in our climate is the redbud, its purpley-pink flowers gracing many roadsides in April. One look at the flowers of any of these plants will betray their pea family heredity.
If you say Rubiaceae family to most folks, you’ll probably be met with a blank look. But many of us consume a brew from one of its species on a daily basis: coffee, from the genus Coffea. Other important members of this family are quinine and ipecac. As for our gardens, hardy cultivars of Gardenia provide potent fragrance, and the Partridgeberry (Mitchella repens) is a native groundcover that will not swallow up entire trees.
A family well known to most gardeners is the Lamiaceae, formerly known at the Labiateae, and more popularly referred to as the Mints. Most people know the mints as herbs with fragrant leaves oppositely held on square stems. (Many members of the family fit this descriptor, although not all.) Peppermint, spearmint and bee-balm are familiar typical mints, with aromatic foliage and the running habit that often has gardeners cursing them. Names of a few other mints read like a well-stocked spice rack: basil, rosemary, sage, savory, marjoram, oregano and thyme. The pungent aromas which humans find so appealing allegedly makes the mints unattractive to deer.
The olive family (Oleaceae) is a bit of surprise with its disparate assortment of species. Of course, there’s the familiar olive tree from the Mediterranean with its well-known fruits and oil. But if you look at its much-planted (and often weedy) cousins the privets you’ll also see similar blue-black fruits and opposite leaves. Ash trees, as well as the forsythias with their early spring yellow explosions, are also members of the olive family.
What about the largest of the plant families? Botanists don’t agree on a clear winner, with two families duking it out for bragging rights. The orchids (Orchidaceae) claim 880 genera and between 21,950 and 26,049 species. Most orchids are tropical, and we see the most extravagant ones in conservatories such as that at Ginter Gardens. But a few orchids also range far into temperate climates. The lady-slippers—Cypripedium is the only genus in the United States—can be found in scattered localities in our area. More common but far less conspicuous is the Cranefly Orchid, Tipularia discolor. They have an unusual life cycle that makes them easier to find in the winter. In the fall a single leaf emerges from each plant’s base and persists until spring. Leaves are typically green and pleated on the upper surface, but purple underneath. A 12- to 15-inch flower stalk with creamy little flowers is easy to miss among the leaf litter but merits closer examination when you find it.
The other possible champ of plant families is the Asteraceae, formerly known as the Compositae, with about 23,000 species spread across 1,620 genera. Composites are so-named for their floral structure, consisting of scores of small flowers typically arranged in a disc-shaped inflorescence. Familiar examples are the sunflower, aster, chrysanthemum, coneflower, black-eyed Susan, marigold, zinnia and the oft-reviled dandelion. Besides these familiar examples from our gardens—and lawns—the composites are important food sources to both humans and birds. We get seeds and oil from sunflowers, leaves from lettuce and flower buds from artichokes, a type of thistle.
Knowing plant families is a bit like genealogy, giving you a better idea of the relatives of the plants in your garden. Of course, like your relatives, you might embrace some, while keeping others hidden in the closet.