17 Plant Family Characteristics

Plant families are separated according to structural differences in flowers, fruit, and seed. Genera that share similar structures are grouped within a particular family. While some plant families, such as Orchidaceae (orchid) and Asteraceae (sunflower family) have several hundred members, others such as Ginkgoaceae (ginkgo) have a single member. As the group with the greatest number of closely related plants, the family taxon provides a starting point for narrowing the search for an unknown plant. In addition to shared morphological characteristics, the family taxon provides information about evolutionary adaptations for growth conditions as well as methods for propagation. One of the most comprehensive references for angiosperms is Flowering Plant Families of the World by V. H. Heywood (2007).  The morphological characteristics for some families and genera commonly found in landscapes and gardens are summarized below. Images of the representative genera are available at this link to the KPU Plant Database [New Tab]^[1] .

Asteraceae – aster, sunflower family

One of the largest families of flowering plants is the aster or sunflower family, Asteraceae. Most of its members are evergreen shrubs or subshrubs or perennial rhizomatous herbs, but tap-rooted or tuberous-rooted perennials, and biennial and annual herbs are also frequent. Common genera of this family include:

• Achillea (yarrow)
• Dahlia (dahlia)
• Jacobaea (dusty miller)
• Leucanthemum (daisy)
• Symphyotrichum (aster)
• Taraxacum (dandelion)

Key identifying characteristics for Asteraceae include an inflorescence that is a composite head with disc florets, (ray florets may or may not be present), and an achene-like cypsela (fruit) with a fringe of hairs or papus. The leaf arrangement may be alternate or opposite, though rarely whorled. Leaf blades are often lobed or toothed and pinnately or palmately veined.

Caryophyllaceae  – pink, carnation family

The pink or carnation family, Caryophyllaceae is a large family of temperate eudicots that are mostly annual, biennial, or perennial herbs and a few subshrubs with woody stems. Many members are flowering ornamentals and some, such as Cerastium may be weedy. Common genera include:

• Cerastium (snow-in-summer)
• Dianthus (pinks, carnations)
• Lychnis (campions)
• Silene (catchflies)

Species in Caryophyllaceae are relatively uniform and recognized by non-succulent stems, swollen stem nodes, and opposite leaves (rarely whorled). Leaf blades are typically simple, lanceolate with entire margins, and without stipules. Flowers are often white or pink, with 4 or 5 petals, and 5 sepals. Petals may be entire, fringed, or deeply cleft and sepals may be free or united. There are usually 5-10 stamens or more and the carpels are united in a common superior ovary. Flowers are terminal and bloom singly or branched in cymes. In some species such as Silene spp., the calyx may be cylindrical and inflated. The fruit is a capsule with many seeds.

Ericaceae – heather family

One of the most common groups of plants in the British Columbia and the Pacific Northwest (PNW) is the heather family, Ericaceae. Family members are mostly temperate woody shrubs and trees, and rarely herbs. Species of Arbutus, Arctostaphylos and Gaultheria are indigenous to the PNW. Some common genera in the Ericaceae family include:

• Calluna (heather)
• Erica (heather or heath)
• Pieris (lily-of-the-valley shrub)
• Rhododendron (including azaleas and rhododendrons)
• Vaccinium (huckleberries and cranberries)

For the most part, ericaceous plants have urn-shaped flowers borne in racemes or panicles. Rhododendron is an exception; they have relatively open, bell-shaped flowers in short racemes (trusses). Other shared characteristics include: fine, off-white shallow roots, an affinity for acid soils, leathery leaves arranged alternately or appearing terminally whorled, rough or peeling bark, and dense wood. While many members are deciduous, genera in this family are among the most recognizable of broadleaf evergreens, both in and out of flower.

Lamiaceae – mint family

The mint family, Lamiaceae is easily recognized because its members exhibit square stems, opposite, often decussate (4-ranked) leaf arrangement, and distinctive two-lipped flowers held in verticillasters (pairs of axillary cymes arising from opposite leaves or bracts and forming a false whorl). The fruit is a nutlet. Family members may be annual or perennial, and are often subshrubs (woody base with soft wooded stems) or entirely herbaceous. Many are highly aromatic, vigorous growers and adapted to propagate easily from stem-cuttings. There are a number of broadleaf evergreen members in Lamiaceae, as listed below:

• Ajuga (carpet-bugle)
• Lamium (dead nettle)
• Lavandula (lavender)
• Rosmarinus (rosemary)
• Salvia (sage)
• Thymus (thyme)

Liliaceae – lily family

Members of the the lily family, Liliaceae are typically perennial herbaceous monocots that grow from bulbs or rhizomes. Leaves are basal, alternate, and sometimes whorled in arrangement with parallel venation.  The inflorescence is a raceme or solitary flower. Flowers are radially symmetrical with parts occurring in 3’s, and separate but undifferentiated sepals and petals (tepals) that may be spotted or striped. The fruit is a capsule. Some of the genera in the lily family include:

• Erythronium (fawn lily)
• Fritillaria (chocolate lily)
• Lilium (lily)
• Tulipa (tulip)

Ranunculaceae – buttercup family

The buttercup family, Ranunculaceae is composed of herbaceous annuals or perennials, woody shrubs, and lianas.  Leaves are typically alternate, sometimes opposite in arrangement, and simple or compound with lobed or dissected margins. The inflorescence is a cyme or solitary flower. Flower sepals and petals are often similar, separate and radially symmetric. Flowers may have few to many petals, often with many stamens and carpels, and produce follicle fruit. Examples of genera in the buttercup family are:

• Aquilegia (columbine)
• Clematis (leather flower)
• Delphinium (larkspur)
• Helleborus (hellebore)
• Ranunculus (buttercup)

Rosaceae – rose family

The rose family, Rosaceae is a large and important family of woody and herbaceous, deciduous and evergreen plants. It is valued for its bush and tree fruits and for many popular horticultural ornamental plants. A few commonly grown rosaceous plants include:

• Cotoneaster (cotoneaster)
• Fragaria (strawberry)
• Malus (crabapple)
• Spiraea (spirea)

Common features of these genera include simple rotate flowers with 5 separate petals, sepals, and stamens, and simple or multiple fleshy or achene fruits. Leave are alternate or basal in arrangement, simple or compound, sometimes toothed and often with stipules. Spines, thorns, and prickles are prevalent in the rose family.

Sapindaceae – soapberry family

The soapberry family, Sapindaceae is a large family of about 140 genera of trees and shrubs, lianas, and vines. Family members such as maples and buckeyes are valued for lumber and ornament. A few examples of sapindaceous plants include:

• Acer (maple)
• Aesculus (buckeye, horse chestnut)
• Koelreuteria (golden rain tree)

Some genera in Sapindaceae, including Acer (maple) are lactiferous, i.e. containing a milky sap. Maples and buckeyes include mostly deciduous trees and shrubs with petiolate, opposite leaves that are often simple, lobed or dissected, or pinnate, ternate, or palmately compound. Leaf venation is palmate or pinnate and leaflet margins may be entire, crenate, serrate, or dentate. The flowers are unisexual or bisexual in racemes, panicles or corymbs. The fruit is typically a distinctive samara in the maples, while the buckeyes produce globular dehiscent capsules with poisonous nuts.

There are several hundred plant families and comprehensive information about additional families is available at this link to the Digital Atlas of Ancient Life Overview of Angiosperm Phylogeny [New Tab]^[2].

Review

Identify the family name for each plant genus.