Plant Families

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Although as horticulturalists and landscapers we are primarily interested in the names and characteristics of plant species and genera, the next higher order of taxonomy for plants, the Family, can also sometimes be useful.  Plants are grouped in families based on morphological and genetic characteristics and while this may be most useful to a botanist or a plant systematist, knowing the plant family characteristics can sometimes aid in identification of unknown specimens, and can sometimes help us to select appropriate plants for a specific landscape use.

Select Families

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Helenium and all the other coneflowers belong to the aster family

Asteraceae

The Asteraceae is the largest family of vascular plants and it should be no surprise that many of the herbaceous plants we cover in this class belong to this family. There are over 22,000 species of plants in over 1,600 genera in this family. 

The type genus of the Asteraceae is the aster, but not the “aster” we study in class. The genus Aster now only contains old world species, the new world species have been split off into a number of new genera and the asters we cover in class, the New England Aster and the New York Aster are now in the genus Symphyotrichum, although they can still be found in the trade as Asters. 

The Asteraceae used to be known as the Compositae. This older name was based on the composite nature of the flowers which is an important characteristic horticulturally.

Characteristics of the Asteraceae

The composite flower head, made up of many florets is the feature that is most distinctive and useful in identifying these plants.

Examples of plants in the Asteraceae we will study in the this class:

Symphyotrichum, Ageratum, Bidens, Calendula, Coreopsis, Dahlia, Heliopsis, Solidago,Tithonia, Zinnia, Echinacea, Rudbeckia, Gazania, Chrysanthemum.

Aster

Aster (Symphyotrichum) has flowers typical of the family.

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Salvia is the largest genus in the Lamiaceae. Flowers have fused petals forming upper and lower lips and fused sepals that are often quite showy. They also sometimes have showy subtending bracts

Lamiaceae

Many ornamental herbaceous perennial and annual plants belong to the family Lamiaceae. The Lamiaceae are commonly known as the mint family. There are about 230 Genera and about 7000 species. The largest genus in the Lamiaceae is Salvia. 

Characteristics of the Lamiaceae

Plants in the lamiaceae have square stems. The flowers are quite distinct with upper and lower lips. Flowers have 5 fused petals and 5 fused sepals. The plants and flowers are often scented. Examples of plants we study include Salvia, Agastache, Dracocephalum, Lamium, Monarda, Thymus, Stachys, Plectranthus, Nepeta.


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Lamium maculatum is typical of plants in the Lamiaceae

Scrophulariaceae

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Digitalis is by some accounts in the Scrophulariaceae but is now properly classified in the Plantaginaceae.

The scrophulariaceae are an interesting family of plants that has been greatly changed by the use of genetics. Genetic typing has demonstrated that many of the plants traditionally associated with the family belong in other families. 

According to the USDA database the Scrophulariaceae now contains 91 genera.

Some examples of plants we are studying that have been reclassified include Digitalis which is now in the Plantaginaceae, Angelonia, Chelone, and Veronica which are also now in the Plantaginaceae at least in some sources. These plants are still listed in the USDA and many other databases as members of the Scrophulariiaceae so for this class you can use either. 

Characteristics of the Scrophulariaceae:

The flowers of plants in the Scrophulariaceae are typically tubular and are often lobed (4-5) or lipped (2). They may have brightly colored bracts. They generally have 2-5 stamens a single style and the fruit is often a capsule.

Plants still in the Scrophulariaceae we study include Sutera, Diascia, and Nemesia, although I’ve seen Nemesia also listed in the Plantaginaceae.

Nemesia flowers  are tubular with distinct upper and lower lobes and  are typical for the Scrophulariaceae

Anthirrhinum

Antirrhinum flowers are tubular with distinct upper and lower lobes

Plantaginaceae

The Plantaginaceae as a family of plants was traditionally rather small but the use of genetic typing has moved many plants from the Schrophulariaceae into this family. 

The name Antirrhinaceae has been proposed for this larger new grouping as well as the name Veronicaceae however the currently accepted name is Plantaginaceae.

Some examples of plants we are studying that have been reclassified include Digitalis Angelonia, Chelone, Antirrhinum, and Veronica. 

Some of these plants are still listed in the USDA and many other databases as members of the Scrophulariiaceae so for this class you can use either. 

Characteristics of the Plantaginaceae:

The flowers of plants in the Plantaginaceae are quite variable but are often tubular and are often lobed with 4 sepals and petals. The corolla is usually 2 lipped. They may have brightly colored bracts. The fruit is often a capsule.

Angelonia also has flowers with distinct upper and lower lobes associated with plants in the Plantaginaceae

Liliaceae

The Liliaceae used to be another sort of “catch all” family with a large number of genera and species. The lily family has also been greatly changed in recent years with many members moved to different families as a result of genetic typing. 

Allium for example is now a separate family the Alliaceae in APG II classification but is in the Amarylidaceae in the APG III classification.  Again the USDA database still lists it as a member of the Liliaceae so either will be accepted in this class. 

Some other genera that we study that have been reclassified include:  Convalliaria (Ruscaceae), Hemerocallis (Asphodelaceae), Hosta ( Agavaceae), Kniphofia (Asphodelaceae) and Liriope (Ruscaceae). 

Common ornamentals remailing in the Liliaceae include; Lilium, Tulipa, and Tricyrtis.

Characteristics of the Liliaceae

The liliaceae are monocots with distinctive bell shaped flowers usually with large conspicuous stamens and anthers and a 3 lobed stigma. Many are very fragrant. 

Lilium has the characteristic flowers that distinguish plants in the Liliaceae

Acanthaceae

A family of about 250 Genera ad about 2500 species. Most are tropical with a few temperate zone species. Plants in this family include Hypoestes, Stobilanthes, Ruellia, Acanthus, and Thunbergia.

Flowers are usually in a spike or raceme with a tubular corolla and 4-5 lobes. Some are subtended by a showy bract.

Acanthus spinosis is a member of the Acanthaceae with very large flowering spikes

Balsaminaceae

A family with 2 genera, Impatiens being the one of landscape value. Plants are succulent and may be annual or perennial. 

Plants in this family include: Impatiens walleriana and Impatiens hawkeri

Flowers are solitary or in cymes. Flowers generally have 5 petals and long spurs.

Impatiens flower showing the long spurs on the back of the flower

Saxifragaceae

About 30 genera and 580 species are in the family. Many are important ornamentals for woodlands and shaded areas. 

Plants in this family include: Astilbe, Berginia, Heuchera, Rodgersia, and Tiarella. Huchera and Tiarella can be hybridized to produce Heucherella

Flowers usually have 5 petals and 10 or sometimes 5 stamens

Heuchera flowers


Plant Families exercise. Answer these questions in the assignment in the Week 3 Canvas module.


What family does Callirhoe involucrata belong to?


Are we studying any other plants in this family?


Write a short description of the features that help to identify plants in this family.


What family does Calibrachoa belong to?


What other plants on our list so far belong to this family?


What other genera and species of economic importance belong to this plant family?

Callirhoe involucrata

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