Why do Botanists Always Tell You the Plant Family? repost

Repost from 2013: Why Botanists Always Tell You the Plant Family

choke cherries, rose family, Rosaceae

People writing about plants are forever sticking the plant family into the discussion.

Ipomoea,  Convolvulaceae,
morning glory family

The photo to the right is a morning glory, Ipomoea (morning glory family, Convolvulaceae)

yarrow, Achillea 
millefolium, 
Asteraceae,
sunflower family

To the left is yarrow, Achillea millefolium, (sunflower family, Asteraceae)

That intended to be helpful. There are at least 300,000 species of land plants. Nobody knows all 300,000. They are organized into classes made of orders, made of families, made of genera and species. Most of the land plants, about 280,000 species, are flowering plants, angiosperms, and are in the same class. There are approximately 60 orders, 400families and 12,000 genera of angiosperms. Orders are so big that they contain very diverse plants. For example the order Asparagales includes orchids, onions and century plants. Writers include the plant family in hopes that you’ll know one plant in the family mentioned and it’ll give you a decent guess what the plant described is like.
  
Here, for example, are capsule descriptions of a few major plant families, not intended to describe their characteristics as much as to prod your memory of them. Plants differ and botanists group them based on those characteristics, so plants in the same family share important characteristics while those in different families seem, and are, different.

rose, Rosa species, rose family, Rosaceae

For example, members of the Rose Family have a ring of five petals around a center and produce a usually fleshy fruit with a few hard seeds inside. Lots of them are shrubs or small trees. Members of the rose family, in addition to roses, are apples, plums, apricots and pears.

Ipomoea sp., Convolvulaceae, 
morning glory family

In contrast, the morning glories are in the family Convolvulaceae. They are mostly vines, with just a few species that are shrubs, small trees or nonviny herbs. The flowers are tubular and tend to be open only for a few hours on a single day. One to several small dark seeds develop inside a thin-walled capsule that dries out when the seeds are ripe. 

   

California oak in flower, 
Quercus sp., Fagaceae, oak family

The oak family, Fagaceae, contains mainly tall trees. Most of the familiar north temperate ones are called oaks, genus Quercus. The family also includes chestnuts, Castanea, southern beeches of the Southern Hemisphere, Nothofagus and some tropical species. The flowers are small, wind-pollinated in temperate regions, sometimes insect-pollinated in the tropics. The fruit with the distinctive acorn cap is shared in the whole family.

The grasses, grass family, Poaceae, are herbs, with a few unusual members such as bamboo. These are lawn grasses like Kentucky bluegrass (Poa praetensis) and crabgrass (Digitaria species), and relatives all over the world. Grass leaves grow from a meristem (growing point) close to or under ground (not up at the stem tips as in, for example, Rosaceae). The flowers are usually on a linear stalk and inconspicuous because they are wind-pollinated. Seeds are the individual grains as in wheat, rye and corn.

grasses along the roadside
grass family Poaceae

asters, sunflower family Asteraceae

Sunflowers, daisies, dandelions, yarrow and asters (and some 1,616 other genera, and over 23,500 species) are in the family Asteraceae, characterized by a “flower” that is actually made up of a lot of smaller flowers in a tight cluster. Most of the plants are herbs, though they can grow to 6’ (2 m).This was is just a glimpse of the diversity of the families, since there more than 400 plant families.

 However, it lets me demonstrate the reason for mentioning the family when mentioning the plant. 

service berry, Amelancher, 
rose family, Rosaceae

 Almonds are in the Rosaceae, the rose family. So you correctly imagine them as similar to roses and apples--in tree shape, flowers and fruit--and certainly not similar to morning glories, oaks, grasses or sunflowers. See pictures: almond tree pictures on Google. That’s how it works. (For those of you who know almonds, another rose family plant you might not know is service berry, Amelancher right).

 In the hierarchical system started by Linnaeus, plant families are named for a genus in that family, with -ceae stuck on the end. The rose family is named using Rosa, the genus of roses, as Rosaceae. Poaceae, the grasses, for the genus Poa, Poaceae. Kentucky bluegrass is Poa praetensis. The morning glory family is named for Convolvulus, the bindweeds, as Convolvulaceae. 

field bindweed, Convolvulus arvensis
Convolvulaceae, morning glory family

The plant family names turn into jaw-breaking words, but the system is coherent. When encountering one, just break it into syllables: Ros ay cee ee, Po ay cee ee, 

Con vol vu lay cee ee (in my accent). 

These family names are capitalized but not italicized. I'm not capitalizing English descriptions--rose family, grass family--because as explained below, choosing which plant to mention is descriptive, not assigned. 

  

Describing the Asteraceae as the sunflower family is not at all required. We often do that because sunflowers are big conspicuous plants that many people know. It is totally valid to say the Asteraceae is the pussytoes family, but many fewer people know what pussytoes look like. That’s why you sometimes see dandelion family or daisy family instead of sunflower family.

chamomile, Asteraceae,
sunflower family

sunflowers, Asteraceae chamomile family                         

pussytoes, Antennaria specues
Asteraceae, sunflower family

Conversely, there are families that are obscure enough that naming a member doesn’t help many people. Madder, Rubia tinctoria, lady’s bedstraw (Galium verum) and sweet woodruff (Galium odoratum) are in the same family, Rubiaceae. However, I don’t believe any of those plants are familiar to most people, so citing the family doesn’t help you visualize the plant I’m talking about, whether I call it the madder family, bedstraw family or woodruff family. I'm so glad we live in the era of digital photography! 

Galium odoratum, sweet woodruff, madder family, Rubiaceae

The number of orders, families, genera and species of plants is under continual revision. See "Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 12, July 2012 [and more or less continuously updated since]." http://www.mobot.org/MOBOT/research/APweb/. for a widely-used source.

Comments and corrections welcome!

Kathy Keeler, A Wandering Botanist

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