The Plant Families You Should Know

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Purpose of the page:

There are a few plant families that have disproportionate impact on us, and you should know which they are. We will discuss only a very limited number of important plant families.

Some Important Families:

Before working with this page, you should work on the Plant Morphology page, as many of the terms introduced there are used here. In addition, you should also work on the Plant Kingdom page to see the overall organization of the plants before working with the family level here.

We are not done with the diversity of flowering plants yet but we will skip over orders of plants and go to families. Why? The answer is simple: for consistency. Up until now, each division covered was composed of plants so similar that you could easily place a plant into it's proper division. Pines, cypresses and junipers are all easy to place in the Coniferophyta. Ferns and mosses are easy to recognize, too. But flowering plants are so diverse that, although they all have flowers and are easy to ID as belonging to the Magnioliophyta, to leave it at that would be to ignore most of the wonderful diversity of plants. Families of plants are often composed of plants similar enough to discuss as a group and so, we will discuss some plant families. Some families. Some taxonomies of the flowering plants have over 200 families and BIOL 4320 students have collected from over 100 different families over the past few years! I want you to be familiar with only a few. I choose them for one or more of three reasons: they include a disproportionately large number of species, they are economically important, or they are wonderful. For some, this last reason might be cause to include all the families, so I will amend it to "disproportionately wonderful so as to counterbalance the important goal of keeping the number of families discussed to the bare minimum."

In order to keep to the criteria above, the number of flowering plant families you will have to know is ten. These are listed below along with a general description of the members of the family and a brief summary of why the family deserved to make the listing.

1. Aceraceae The Maple Family. Over 150 species. Maples are tree, vines (rarely) or shrubs. We normally recognize maples by the shape of their simple or compound, opposite, palmately veined leaves. Look at the pictures of leaves at the Brandeis site at the end of this paragraph to see some maple leaves. Very few trees in this area (perhaps Sycamore and Tulip Poplar) have leaves similar, so they are easy to identify. A confusion for beginning students it the name "Sycamore." Sycamore can refer to either Platanus occidentalis, also called the Plane Tree, or to Acer pseudoplatanus, often called Sycamore but more properly called Mock Sycamore. Be careful. The flowers are usually not very showy but the dry fruits are double samaras, two fruits joined together. They often rotate like a helicopter when they fall from the tree and this "helicoptering" can carry the seed from the mother tree. This not a very important group agriculturally beyond maple syrup. The wood is important in furniture manufacture. The reason we include it here is that it is an important member of our forest and you are almost sure to include one or more maples in your collection. More on maples can be found at the Wikipedia site, the Digital Flowers database of the U. of Illinois, and at the DELTA site (see bottom of page for more on DELTA). There are some shots of maple leaves at Brandeis U. Biology.
2. Cactaceae The Cactus Family. Over 2000 species. These are stem succulents because they store water in their stems. Except for a very few species in a single genus, they also have no mature leaves (sometimes new growth will briefly have succulent leaves attached), although some of the stems may be flattened and look a little like leaves (think of the Christmas cactus sold during the holidays). The nodes produce spines instead of leaves and their anatomy is unusual enough that they get the name of aureoles. They are included here because they are one of only two families found only in North and South America and much of my research has involved things that live in cacti.  Cacti are food for humans and livestock.  The fruits are most often eaten but the seeds can be roasted and ground into flour.  Some prickly pear pads are eaten after being cleaned of spines and outer cuticle (try a nopal salad next time you are in a good Mexican restaurant).  As livestock feed in dry areas, cacti can provide both food and water at the same time.  Some cactus flesh contains toxins (alkaloids and other lipids) and these have been exploited as poisons to kill fish and as medicines (as emetics or laxatives).  Some of the toxins are hallucinogenic.  There are excellent websites on cacti at Wikipedia , at the DELTA taxonomy site (see bottom of page for more on the DELTA project), and at Botany-Online. There are pictures of cacti at desert tropicals and at a page by Mark Olson. There are beautiful pictures of cactus flowers at the On Closer Inspection site. Take a look at these both for their beauty and to see that they all have the same basic structure. Once you have really looked at a cactus blossom, you can never fail to recognize them.
3. Compositae   The Composite or Daisy Family. Over 20,000 species in over 900 genera.   The members of this large family are most often herbs, although there are a few bushes and trees in the family (no trees or bushes are native here).   The leaves vary a lot and can be either simple of compound, alternate or whorled.  The best way to recognize a member of the Compositae is to see its flower, which is always many flowers fused together into a flower head. Each flower (called a floret) sits on the fused receptacle, which is often covered by bracts.  The flowers may be tiny but the flower head can be large (sunflowers belong to this family).  The flowers along the periphery of the flower head fuse their five petals into a strap-like petal that sticks out from the flower head.  These are called rays and the florets that produce them ray florets.  The more central florets usually produce very short tube corollas.  The Compositae is included here due to the large size of the family.   In addition, although we eat rather a small number of species out of this large family (artichokes, lettuce, endive, radicchio, Jerusalem artichoke, and sunflower seeds) we have cultivated many ornamentals from the family (marigold, zinnia, chrysanthemum, dahlia, and many others).  Good sites are found at Botany-Online, Oregon State U. (called the Asteraceae here), Wildflowers and Weeds (which has lots of good pictures), and Wikipedia.
4. Curcurbitaceae   The Gourd or Melon Family. Over 800 species.  Most melons are annual vines with palmately-veined, simple, opposite leaves with large lobes and lots of hairs stiffened into prickles.  The solitary flowers are large with 5 parts and often separate male and female flowers are found on the same plant.  The fruit is a pepo or more commonly, a melon.  The family is important agriculturally.  Squash, zucchini, cantaloupes, honeydews, cucumbers, luffas, gourds, pumpkins, hubbards, butternut squash, acorn squash, calabash, and watermelons are all members of the family.  They often produce triterpenoid cucurbitacins, bitter-tasting oils that give the fruits a bad taste.  More on melons can be found at the Wikipedia site, the Digital Flowers database of the U. of Illinois, Biology Online, and at the DELTA site (see bottom of page for more on DELTA).
5. Fabaceae   The Pea Family. Over 18,000 species.  Members of this family are also called legumes.  In fact, the family used to be called the Leguminosae and some still use the term.  As an additional bit of confusion, some taxonomists have elevated some of the subgroups within the family up to family status, so Mimosa trees are in the Fabaceae in some classifications and and in their own family, the Mimosaceae.  We will use the more inclusive form.  Members of the family are everything from herbs to trees.  The leaves are usually alternate and pinnately compound (palmately compound and simple leaves are also found but not very commonly).  There are usually stipules at the base of the petioles.  The flowers are most often perfect with a single, simple ovary. It is this ovary that develops into the fruit type all Fabaceae have in common: the legume.   This is a pea pod.  Some pods do not dehisce (split open) as they dry out but most do and they split along both sides of the pod.

   The family is important in more than one way.   It is perhaps the second most important family agriculturally.  Peas, beans of all sorts (and there are many types of beans from those whose pod is edible to those whose seeds are edible), tamarind, carob, lentils, licorice, and peanuts.  Peanuts are unusual in that the stem with the flower grows downward after fertilization and the fruits develop underground (many in the South call them ground nuts).  Beans are important sources of proteins for those who either forgo animal proteins or cannot obtain animal protein.  Soy beans are particularly high in protein and have been adopted world-wide as animal feed.  The family includes many members that nodulate (see link to a pdf file if this is confusing - just read the introduction pages) and so growing them can increase the level of biologically useful nitrogen in the soil. This is often a nutrient in very limited supply and so soil fertility usually increases if clover or alfalfa are grown on it.  The clover and alfalfa are then harvested as winter forage for cattle.  Kudzu is a member of the family brought to the US to control erosion on hillsides.  It has become a problem is some areas by overgrowing trees but it does have edible fruits and the leaves are good animal forage.  Finally, many ornamentals belong to the family, from flowers to trees.  More on the Fabaceae can be found at the Wikipedia site, the Digital Flowers database of the U. of Illinois, Reed College, and at the DELTA site (see bottom of page for more on DELTA) uses the name Leguminosae.

6. Fagaceae The Oak or Beech Family. Over 1000 species. This is a family of trees, including the dominant trees in our local forests, and a few shrubs. The trees are mostly deciduous but some evergreens are found in the family. The leaves are simple and alternate. Stipules are usually present (for some pictures of leaves from the family go to this link). The flowers are often less than spectacular (an exception is the European chestnut). The fruits are nuts surrounded by a cupule, which develops from the involucre (a set of bracts that surrounds a flower or flower head). The cupule is the acorn's cup or the husk around a hickory nut. The economic importance of the family comes from the nuts produced by chestnut trees and by the valuable hardwood lumber cut from many of the species. We are interested in the family because they are the dominant trees in local forests and you are sure to have a few members of the family in your collection. The family includes the beeches, oaks, and chinquapins. More on the family can be found at the Wikipedia site, the Digital Flowers database of the U. of Illinois, in an online article by Henrietta Chambers in the journal Oregon Flora Newsletter, and at the DELTA site (see bottom of page for more on DELTA).
7. Orchidaceae   The Orchid Family. Over 25,000 species (over 100,000 hybrids and cultivars are known).  This is the largest family of plants. Many species have flowers that are capable of pollination by one or two species of insect only and it is thought that the tendency to form these specific pollination mutualisms have given rise to so many species of orchids.  The plants are herbs or vines (vines are also called lianas).  Most are terrestrial but many are epiphytes growing on other plants (not parasites but just using the host as a way to get more sunlight).  This is a monocot family and the leaves tend to be strap-like with parallel veination.  The flowers are zygomorphous (bilaterally symmetric) and can be quite complex.  An easy-to-see feature is the lip or labellum, a single tounge-like or bag-like structure that comes from the center of the flower.  Interest in orchids stems more from a sense of beauty that from hunger.  Orchids do give us an important spice, vanilla.  Some orchids have tubers at the base of the leaves and one species in Turkey is the basis for a popular kind of ice cream.  Orchid flowers are prized world-wide and have lead to intense collecting and breeding. When humans transfer pollen rather than insects, hybrids form readily and flower breeders have exploited this tendency to produce more hybrids than there are species! More information on orchids can be found at Botany-Online, at Wikipedia, at Reed College, and at the Delta database (see bottom of page for more on the delta system) page on orchids.
8. Poaceae   The Grass Family. Between 8000 and 10,000 species. Grass family members are herbs, except for bamboo, which is tall but still a herb.  Grasses, although found in all habitats from deserts to rain forests, dominate where there is some rainfall, often strongly seasonal, but not enough to support forests (they are so dominant we call this biome the grassland).  Many grasses employ the C₄ pathway, which reduces photorespiration and water loss through transpiration (to see why, follow this link).   This is one of a suite of adaptations to low-water stress conditions.   Many plants spread through underground rhizomes or above ground stolons.  The stems have hollow internodes (the areas between the nodes) and are often hardened by the deposition of silica (SiO₂, glass).  This anti-herbivore adaptation is also found in the leaves, which can give the edge of a leaf the sharpness and strength to cut fingers, so watch out.  The leaves have no petioles and the leaf base attaches in a strip around the node.  The meristem (growing region) of the leaf is at the base instead of at the tip (as it is in the vast majority of plants).   This is an adaptation to grazing, where the top of the leaf can be removed all at once but the leaf can regrow from the base.  The blade of the leaf often forms a sheath that surrounds the stem before it splits and the flat, strap-like leaf bends away from the stem.  If you look closely at the base, there is often a small extension from the base called a ligule.   This is a monocot family and grass leaves are classically parallel veined.   The flowers are small and wind-pollinated, so they tend to be inconspicuous.  Petals have been lost and each floret is surrounded by bracts (each of which have separate names we won't use here).  The fruits form on the floret spikelets, which gives them the look we all know from wheat or corn ears.

   It is almost impossible to overstate the importance of the Poaceae to both our everyday lives and our history.  We humans gave up the hunter-gatherer lifestyle and settled into permanent communities when we began to cultivate crops.  Where ever civilizations grew, the staple crop was almost always a grass (potatoes in the mountains of South America are an exception).  We sustain a population of billions mostly on grass crops (or meat raised on grasses). The Poaceae contains most of our staple food crops: wheat, corn & rice.  In addition, beer is brewed from barley (which is also eaten), and sugar can be processed from sugar cane or sorghum (also called milo), although beets are also an important source of sugar.  Grasses are important in preserving soils with their tight network of fibrous roots (see the Vetiver page for a new application of this technology).  Grasses are also important ornamentals and might be in your collection. More on the grasses at Wikipedia, a slightly diffferent version of the Wikipedia page at Biocrawler, at the What-you-need-to-know-about page, at Oregon State U., and a page that compares monocot families with a brief description of grasses and links to grass pictures at the U. of Tasmania. There is a pdf that describes the grass family available for downloading at the U. of Texas.

9. Rosaceae The Rose Family. Over 3000 species. Members of this family can be herbs, shrubs, vines or, very often, trees. The leaves are usually alternately placed, can be compound or simple, and usually stipules are present at the base of the petiole. The flowers are 5 part or multiples of 5, solitary, with little fusion of petals and lots of stamens. The fruits are most often drupes but pomes are common and some achenes (the fruit is a seed covered with some dried layers of tissue called the pericarp) are found in the family. It is the fruits that make this family importance to us. Cherries, plums, and peaches are all drupes. Sometimes drupes are aggregated into a single structure as in raspberries, blackberries, black raspberries, dewberries, loganberries, cloudberries, salmonberries, etc. Almonds are a nut crop from a member of the family. Strawberries are rose family members with achenes as fruits (they are the little black "seeds" on the outside are the strawberry). What we eat as the strawberry is botanically called the accessory fruit. Of course, roses are among the most popular ornamental plants in temperate zones. More information on the rose family can be found at Botany-Online, at Wikipedia, at Reed College, and at the Delta database (see bottom of page for more on the delta system) page on the Rose Family.
10. Solanaceae The Nightshade or Potato Family. Over 2500 species. These are mostly herbs (a few are vines or small trees) with simple leaves, often with hairs or prickles on them, arranged alternately (may appear opposite near flowers). The flowers parts are usually in fives with the petals and sepals each fused at the base. The petals are often completely fused into a tube-like corolla and the ovary is inferior. The fruits are either fleshy berries (tomatoes) or dry capsules (peppers) that split open when totally dry. The family has a long history of uses for humans, which is why it qualifies as one of the ten families. The potatoes, tomatoes, eggplant, peppers, chilies, paprika, mandrake, and tomatillo are all members of the family. Many family members produce alkaloids, secondary chemicals found in many plant families. The alkaloids in the Solanaceae often have toxic or pharmacologic effects. Jimson weed (loco weed) and deadly nightshade (belladonna) can kill if too much is ingested. Even the green portion of potatoes is toxic, although we usually don't eat enough to affect us. Belladonna is used to dilate eyes by ophthalmologists. Tobacco is a member of the family and nicotine is the alkaloid it produces. Finally, the petunia is a member of the family and what would spring in Tennessee be without gardeners setting out petunias? Good websites on the family are at Botanical-Online, Oregon State U. , Wikipedia, and the site maintained by J. A. M. van Balken, a man dedicated to the Solanaceae. You can see a flower with five stamens and a fused corolla on the main page of his website.

There is an interesting online plant key system for families based on DELTA (DEscription Language for TAxonomy) developed by MJ Dallwitz of Australia's CSIRO (Commonwealth Scientific and Industrial Research Organization) and colleagues. It requires that you download a small program (for Windows only) which accesses an online database so that the information is always up-to-date. You can get the program and instructions at the DELTA homepage.

Last updated July 9, 2013