By Cynthia B. Lauer, Master Gardener, SCMG
In this article, we explore three more taxonomic families of plants that are commonly found in our gardens and kitchens. Common names are used along with their botanical names based on the binomial system described in Part I. The watermelon, for example, is Citrullus lanatus; the first word denotes the genus, the second the species. In the hierarchy of taxonomy, family is one category above the level of genus and can include dozens (or hundreds) of individual genera. Genera can include dozens (or hundreds) of species. Learning about taxonomy reveals the close relationship between chili peppers and petunias or between cola and hibiscus to give just two examples.
Cukes and Their Cousins: The Cucurbitaceae Family
What comes to mind when you hear the ambitious word Cucurbitaceae? Cucumbers, likely. But this diverse family of plants also includes all of the melons, all of the squashes, zucchini, and the loofah that is used as a natural sponge. The cucurbits or gourd family number about 1000 species in around 100 genera. When you think about it, their common features become obvious. Most are annual vines with large solitary yellow or white flowers emerging from the end of individual stems. The plants grow either prostrate along the ground or climb using tendrils.
Squashes, Alexas_Fotos, Pixabay
The outer layer of the fruit can range from the leathery skin of cucumbers to the hard rind of mature pumpkins. In most species, the fruit is a fleshy many-seeded berry and can often be very large. The fruit can hang from the plant but heavier varieties rest on the ground. The flesh ranges from the fleshiness of cucumbers to the dryness of some squashes. They can contain anywhere from several to hundreds of seeds. The seeds are flat and, in some varieties, contain edible and medicinal seed oil. Summer squashes are prematurely harvested and softer, and the rind may be cooked and eaten with the flesh. Due to the mature nature of the winter squash, the rind is too hard to be eaten. Only the cooked flesh of winter squash is consumed.
Cucurbitaceae is the second largest fruit and vegetable family and its members are among the most important edible plants in the world next only to Solanaceae (discussed below). They are grown around the tropics and in temperate areas. The development of the whole-genome sequences of Cucurbitaceae has led to plant breeding programs to improve key traits of the family. Pathogen resistance, fruit size, mass, color, texture, length, shape, rind form, ripening behavior, sugar content, bitterness, flavor, and tendrils have all been manipulated for human needs.
Most species in this family are extremely sensitive to cold temperatures, a factor that limits their area of cultivation. Cucurbits should be grown in warm fertile soil that is well irrigated. They need an immense amount of heat, long days of light, and a lot of moisture. Ample space is necessary both for the roots and for the plant to expand above ground. They are difficult to grow in small gardens because of their demand for space. One option is to use a trellis or other support. Alternatively, the use of dwarf or bush cucurbits may be practical.
Beans and More Beans: The Fabaceae Family
Fabaceae has traditionally been divided into three subfamilies one of which, Faboideae, is legumes consisting of about 475 genera and nearly 14,000 species. It consists mostly of herbaceous plants plus some trees and shrubs that bear fruit in the form of a bean or legume. Examples of genera and species are beans (Phaseolus), peas (Vicia, Pisum), chickpeas (Cicer arietinum), sweet peas (Lathyrus), lentils (Lens culinaris), peanuts (Arachis hypogaea), soybeans (Glycine max), alfalfa (Medicago), and clover (Trifolium). Some gardeners may not expect to find these other members of the family—honey locust (Gleditsia), black locust (Robinia pseudoacacia), Kentucky coffee tree (Gymnocladus dioica), redbud (Cercis), kudzu vine (Pueraria montana), licorice (Glycyrrhiza glabra), lupine (Lupinus), mesquite (Prosopsis), mimosa (Mimosa), tamarind (Tamarindus indica), rooibos (Aspalanthus linearis), and wisteria (Wisteria).
A few members of the bean family such as scotch broom (Cytisus scoparius), Chinese wisteria (Wisteria sinensis), vetch (Vicia sativa), kudzu (Pueraria montana), and black medick (Medicago lupilina) are known for their invasiveness. But legumes are better known for their role in fixing nitrogen in soil. This is how it works: although elemental nitrogen makes up about 80 percent of the atmosphere, it is not directly available to living organisms until it is turned into nitrates or ammonia compounds. Beans accomplish through a special relationship with Rhizobium bacteria that lives in their roots. Through a symbiotic relationship, nitrogen from the air is fixed into a compound that can be absorbed by plants once the roots of the host plant decay. When this occurs, nitrogen products are released into the soil. Most of our forests, prairies, and deserts could not exist without the nitrogen produced by legumes.
Rhizobium bacteria on roots of Acacia, (Scot Nelson), Flickr, Creative Commons
Legume seeds constitute a part of the diet of nearly all human societies and most of the protein for people living in developing regions. However, some legumes carry health risks; positive identification and reliable information about use and preparation is essential. Vetch and clover, for example, can affect the liver and cause photosensitivity. Aflotoxin is a toxic fungus that can occur on peanuts and other nuts. Chemical substances such as alkaloids, flavonoids, and tannins produced by legumes are often poisonous in animals. The medical potential of some of these substances has been extensively studied.
A Diverse Palate: The Solanaceae Family
Most of the species in the potato or nightshade family are native to western South America extending up into Central America and Mexico. There is disagreement about the number of species that may range from 1,500 to 4,000. Examples of the edible plants are potatoes (Solanum tuberosum), tomato (Solanum lycopersicum), chili peppers and sweet peppers (Capsicum), eggplant (Solanum melongena), tomatillo (Physalis), and ground cherries (Physalis spp.). Angel trumpet (Brugmansia), tobacco (Nicotiana tabacum and N. rustica), petunia (Petunia), jimsonweed (Datura), belladonna (Atropa belladonna), and mandrake (genus Mandragora) are other important members of the family.
Solanaceae flowers generally have the reproductive organs of both sexes present in the same flower. Floral parts occur in multiples of four or five. The fruit is a berry or capsule and contains many seeds. The family contains both wide-open flowers for attracting generalist pollinators, and irregular corollas with narrow openings adapted to specialized bees. Several groups have tubular or night-scented corollas that attract moths.
Potatoes mostly grow in the uplands of western South America but with distinctive species in Mexico and the southwestern United States. Today, most potatoes are a single species but several other tuber-bearing species are still cultivated by indigenous peoples in the upland regions of Peru. Peppers were domesticated in Mexico where greatest number of species are found. The word ‘chili’ is from the native Mexican-language word for the Capsicum plant; capsaicin is the pungent substance found in the seeds of hot peppers. There are five species of domesticated peppers—sweet peppers (Capsicum annuum), Peruvian peppers (C. baccatum), habanero peppers (C. chinense), hot peppers (C. frutescens), and tree peppers (C. pubescens). Black pepper is from the vine Piper nigrum, a plant unrelated to Solanaceae.
Consumption of the fruit and sometimes the leaves of Solanum plants can be extremely dangerous. Tobacco contains a convulsant poison, while tomato, horse nettle, and potato can cause contact dermatitis. Steroidal saponins (toxic plant-derived organic chemicals) and toxic alkaloids may also be found in some species. Deaths have been attributed to green-fleshed potatoes, belladonna, the anthers of long-tubed daturas, and other species. Tobacco has been linked to cancer and other illnesses. A final example demonstrates the diversity of this plant family: with its thick tuberous roots resembling the human form, mandrake contains a powerful alkaloid that has been used both as an anesthetic and a hallucinogen.
