By Cynthia B. Lauer, Master Gardener, SCMG
In this article, we explore our final three taxonomic families of plants. Common names are used along with their botanical names based on the binomial system described in Part I. The black cherry tree, for example, is Prunus serotina while the black-eyed Susan is Rudbeckia hirta or R. fulgida; the first word denotes the genus, the second the species. An appreciation of taxonomy reveals the close relationship between iceberg lettuce and zinnias, or between turfgrass and sugarcane to give just two examples.
The Essential Grains: The Poaceae Family
Poaceae is a very large plant family with around 12,000 species and roughly 800 genera. It contains the cereal crops, bamboos, and all of the grasses—prairie, steppe, savannah, pasture, and lawn. With domestication, bread wheat (Triticum aestivum), barley (Hordeum vulgare), oats (Avena sativa), and rye (Secale cereale) in the Middle East, sorghum (Sorghum bicolor) in Africa, rice (Oryza sativa) in Southeast Asia, and corn/maize (Zea mays) in Central America have supported many civilizations. Tef (Eragrostis), millet (Pennisetum), and wild rice (Zizania) belong in the family as do bamboo (many genera), reed grass (Phragmites), and sugarcane (Saccharum).
Grasslands are estimated to constitute 40.5% of the land area of the earth excluding Greenland and Antarctica. Grasses are an important part of the vegetation in many habitats including wetlands, forests, tundra, desert, freshwater and marine habitats at all but the highest elevations. Ecologically and economically, Poaceae is the most important of all plant families. Their remarkable adaptability means they are also some of the world’s most pernicious weeds. Phragmites australis, giant reed grass, has the widest geographic range of any flowering plant and is regarded by some to be the world’s worst invasive species. Its rhizomes rapidly infest wet soils of ponds, streams, and banks to the eventual exclusion of almost all other plants.
Grasses can be perennial or annual. Their roots are fine and fibrous; individual plants may be solitary or densely clumped. Many grasses produce horizontal stems, either below ground (rhizomes) or above ground (stolons). Grass stems range from about 2 centimetres for some species found in severe climates to 40 metres in bamboos. Having no sepals or petals, flowers hang from spikelets grouped into panicles or spikes. Besides wind-pollination, seeds are also dispersed by passing animals when bristles attach to their fur. Grasses have multiple methods of reproduction—cross-pollination between plants, self-fertilization, and asexual reproduction in which a clone is reproduced. Grasses are unusual in that growth occurs not at the top like most flowering plants, but at the base of each stem. This is why they quickly recover when they are cut down by fire, mowing, or grazing.About 35 species of grass have been domesticated. For example, more than 200 cultivars of wheat are grown in North America. In world production, the four best-known crops—sugarcane, wheat, rice, and corn/maize—provide more than half of all calories consumed by humans. These cereals constitute our major source of carbohydrates: rice in southern and eastern Asia; maize in Central and South America; wheat and barley in Europe, northern Asia and the Americas. Alcoholic beverages are distilled from crop grasses: barley provides beer malt, rice is used in the production of sake, and corn for bourbon. Wheat, rye, corn, and barley contribute to the making of whiskeys and vodka. Other grasses are used for livestock feed and bedding, soil stabilization, recreation areas, golf courses, building materials (eg. bamboo, thatch, straw), insulation, and fuel (eg. ethanol).
Fruit for All: The Rosaceae Family
With over 2,500 species in more than 90 genera, plants in the Rosaceae family are highly valued. Mostly found in north temperate zones worldwide, this family of plants grows in a wide variety of habitats. Generally woody plants, most are shrubs or small to medium-size trees some of which have thorns, spines, or prickles to discourage herbivores. The genus Rubus are usually arching shrubs or rambling vines.
Rosaceae includes apples (Malus spp.), pears (Pyrus spp.), plums, cherries, apricots, peaches, nectarines, almonds (Prunus), quince (Cydonia), strawberries (Fragaria), and raspberries (Rubus). Birds and other wildlife forage wild serviceberries (Amelanchier spp.), hawthorns (Crataegus spp.) and mountain ash (Sorbus spp.). Ornamentals include lady’s mantle (Alchemilla mollis), cotoneaster, kerria, geum, cinquefoil (Potentilla), goatsbeard (Aruncus), ninebark (Physocarpus), spirea (Spiraea), and, of course, roses (Rosa).
Flowering apricot, Cynthia Lauer
The family is usually divided into four subfamilies based on fruit type: follicles (spirea), aggregates (raspberry), nuts (almond), achenes (strawberry), drupes (peach), pomes (apple), or hips (rose). Flowers are showy and symmetrical, typically flat or shallowly cup-shaped, and appear as panicles, racemes, spikes, cymes, solitary flowers, or other forms. They usually have five sepals and five petals and carry both male and female reproductive parts.
Numerous members of the genus Prunus host butterflies. Cherries, plums, and nectarines host the Red Spotted Purple butterfly, while chokecherry (Prunus virginiana) and wild black cherry (Prunus serotina) host the Tiger Swallowtail butterfly and the Coral Hairstreak butterfly. Cherries and the American plum (Prunus americana) host the Striped Hairstreak butterfly. The Cecropia, Promethea, Apple Sphinx, and many other species of moths find hosts in other members of the Rosaceae family.
For the Love of Flowers: The Asteraceae Family
With species running well over 30,000, Asteraceae is the largest family of flowering plants. It is estimated that the family represents around 10% of all flowering species. Their impressive biodiversity covers all habitats and regions on the planet except Antarctica. Research determining the number and traits of the Asteraceae family continues today. One result is that most of the North American plants in the original genus Aster are now in the genera Symphyotrichum or Eurybia. This also explains why Joe Pye weed is no longer known as Eupatorium but Eutrochium. DNA has taught us that species long thought to be closely related actually are not. Their similarities evolved independently. For example, North American asters are more closely related to goldenrods than to native European and Asian asters. What had been known as Aster ptarmicoides turns out to be a white-rayed species of goldenrod, Solidago bicolor.
Phylogenetic research revealed that this plant is a white-rayed species of goldenrod now called Solidago bicolor instead of Aster ptarmicoides.
Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0
The chief characteristic of Asteraceae are composite flowers that, from a distance, look like a single flower. However, close inspection shows that the flower head is actually a cluster of tiny flowers. The “petals” are individual strap-shaped flowers called “ray flowers” surrounding a mass of smaller circular shaped individual flowers called “disc flowers”. In Greek, the word “aster” means “star” referring to a flower head that looks like a star surrounded by rays.
Most members of Asteraceae are herbaceous but a significant number are also shrubs, vines, or trees. They are generally easy to distinguish from other plants because of shared characteristics. Most of these plants produce taproots and have erect stems but there are exceptions. Some possess fibrous root systems and have prostrate stems or woody stems with a great deal of leaf variation.
Asteraceae is an economically important family providing products such as cooking oils, lettuce, sunflower seeds, sweetening agents, coffee substitutes, and herbal teas. Of horticultural importance are marigold (Tagetes), calendula, cone flowers (Echinacea), black-eyed Susan (Rudbeckia), daisies (Leucanthemum), chrysanthemums, dahlias, and zinnias. Cultivated and wild food crops include safflower (Carthamus tinctorius), sunflower (Helianthus annuus), lettuce (Lactuca sativa), chicory (Cichorium intybus), artichoke (Cynara scolymus), and Jerusalem artichoke (Helianthus tuberosus). Also found in the family are blanket flower, helenium, yarrow, burdock, coreopsis, cosmos, goldenrods, wormwood, boneset and many other species.
Invasive members of the family include cornflower (Centaurea spp.), ragweed (Ambrosia spp.), Canada thistle and Bull thistle (Cirsium arvense, C. vulgare), oxeye daisy (Leucanthemum vulgare), coltsfoot (Tussilago farfara), dandelion (Taraxacum officinale) among others.
