The Aster Family (part 3)

There are three types of aster family flower heads, named according to the type(s) of florets present.

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If both types of florets (ray or ligulate and disk) are present in a head, the arrangement is termed radiate.

Verbesina alternifolia
(wingstem)

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If a head contains rays only, it is called ligulate.

Hieracium venosum
(rattlesnake weed)

 

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And if only disk florets are present, a head is called discoid.

Vernonia noveboracensis
(New York ironweed)

 

Another characteristic of aster flower heads is the presence of phyllaries.

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Symphyotrichum species, possibly S. oblongifolium 
(aster)

 

 

At the base of a flowerhead there’s a whorl of bracts (modified leaves), called an involucre. In aster family plants only, the individual leaf-like structures are called phyllaries. The number of phyllaries, how they’re arranged (how many rows), the shape, presence of hairs, and other fine details are characteristics used to distinguish certain species from others [see this recent post about tickseed].

Symphyotrichum species
(aster)

next: aster fruits/seeds

The Aster Family (part 2)

Aster family flower anatomy gets complicated and the subject is full of jargon. Here’s a photo-illustrated primer.

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Aster family plants have flowers by the dozens or hundreds, clustered together in heads. This plant —>
is Helenium flexuosum (sneezeweed), with one open head and one still-developing head. What appear to be yellow petals are actually individual ray flowers. If you click on the image and zoom in, you can clearly see several individual flowers at the bottom, each one three-lobed. The purplish, nearly spherical center part is composed of disk flowers. The ones on the bottom half are open, with two-parted stigmas protruding, while the upper half holds still-closed buds.

“Ray flower” is a general term. There are actually two different types of rays: ray florets and ligulate florets. Both are tubular-shaped at the bottom, and flatten out towards the top. Ray florets can be sterile or pistillate (that is, female*), and have 2 or 3 teeth or lobes at the end, Ligulate florets are perfect (that is, bisexual: containing both male and female parts*), and often have 5 teeth or lobes.

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Smallanthus uvedalia (large-flowered leafcup), showing 10 ray florets and 13 open disk florets
[click on the picture to zoom in and see the details]

 

The central flowers in a head are called disk florets. These consist of five petals fused together, so that they look like a single five-lobed tube; the stigma often protrudes, sometimes dramatically. The central disk can be more or less flat to almost spherical (as in the first photo).

next time: the three types of aster flower heads

 

*with apologies to my friend Linda for anthropomorphizing

The Aster Family (part one)

From golden ragwort in April to goldentop in October, about one in five flowering plant species that I find in the Maryland Piedmont is in the aster family.

It’s unknown how many plant species there are altogether: discoveries still happen, and of course there’s taxonomic uncertainty. But experts believe that there are about 352,000 flowering plant species (angiosperms), and of the other major plant groups, there are an estimated 1,000 species of conifers and conifer allies (gymnosperms), 13,000 species of ferns and fern allies (pteridophytes), and 20,000 species of mosses and liverworts (bryophytes). [The Plant List]. So it’s probably safe to say that flowering plant species outnumber all other plant species combined by an order of magnitude.

Of the flowering plant families, the Asteraceae is probably the largest with about 23,600 species in 1,620 genera. [Encyclopedia of Life]  Whether or not it actually is the largest depends on the current state of taxonomic science; the other contender is the Orchidaceae.

There are 2,401 native Asteraceae species in North America. [BONAP] The Maryland Biodiversity Project lists 373 Asteraceae species (native and alien) in Maryland, and by my very rough estimate, about half of these can be found in the Piedmont.

So what are the characteristics of aster family flowers?  Have a look at this Jerusalem artichoke:

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How many flowers do you see? If I zoom in I can see about 21, not counting the unopened buds.

Wondering how that can be? Here’s a clue: an older but still accepted name for this family is Compositae, or composites. Plants in this family bear heads that appear to be single flowers, but these heads comprise from several dozen to several hundred individual flowers.

next time: aster family floral morphology

This post is dedicated to my friends Cheryl and Barry, who independent of each other gave me the idea to write about plant families during the dormant season. 

October Report

I can hardly believe it’s been more than a month since my last post. Sadly, I’ve only been out hiking three times since then. In mid-October, there isn’t a whole lot of variety to see.

Serpentine Barrens Conservation Park, October 17:

  • asters, blue and white, unknown species
  • silver rod (Solidago bicolor)
  • tickseed sunflower (Bidens polylepis)
  • hyssop-leaved thoroughwort (Eupatorium hyssopifolium)
  • goldenrod (unknown species)

Carderock, October 17:

  • white snakeroot (Ageratina altissima)
  • flax-leaved aster (Ionactis linariifolia)
  • calico aster (Symphyotrichum lateriflorum)
  • blue stem goldenrod (Solidago caesia)
  • zigzag goldenrod (Solidago flexicaulis)
  • silver rod (Solidago bicolor)

Cabin John Trail, October 14:

  • beech drops (Epifagus virginiana)
  • seedpods on downy rattlesnake plantain (Goodyera pubescens)
  • common blue wood aster (Symphyotrichum cordifolium)
  • white wood aster (Eurybia divaricata)
  • other white aster (unknown species)

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common blue wood aster
Symphyotrichum cordifolium

Common blue wood aster, aka heart-leaved aster, is found all over the eastern US and Canada, with some occurences in the midwest, mostly between the Missouri and Mississippi Rivers, and also in British Columbia. The taxonomy of several species closely related to this one is in flux*, so beware if you’re using an older guidebook to try to identify asters that you find. You might not be able to say for certain which species is is, only which genus. For that matter, the older guidebooks will still give the genus as Aster rather than Symphyotrichum.

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white wood aster
Eurybia divaricata

White wood aster has similar leaves to common blue aster, but obviously different flowers. This species is not as widespread, occurring mostly in the greater Appalachian region, from New Hampshire to Alabama (and possibly in Quebec and Ontario).

BONAP and the Maryland Biodiversity Project agree that common blue wood aster can be found in Montgomery and Frederick Counties in Maryland, but disagree where else in the state it grows. Both sources show white wood aster growing in more counties in Maryland. Each of these species grows one to three feet tall, common blue in moist to dry woodlands, white wood in drier areas.  The patch of common blue pictured below is along the Cabin John Trail, near the southern end. It really just lights up the whole area.

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*see my post last year on the subject: Are Asters Really Asters?