Weakley Flora to the Rescue! (With a Primer on Using Botanical Keys)

upper stpem, leaves, and inflorescence

upper stem, leaves, and inflorescence

The day after writing the previous post, I returned to Serpentine Barrens Conservation Park armed with a 10X lens, a small knife, a ruler, a notebook, and most important, a printout of page 1126 of the Flora of the Southern and Mid-Atlantic States by Alan S. Weakley, determined to key out my unknown goldenrod species.

Success! I keyed it out in the field, but collected a sample to photograph at home with the macro lens.

If you’re interested in how botanical keys work, keep reading. If you just want to know which species it is, skip to the end.

The first couplet in Weakley’s key reads:

1  Leaves with numerous slightly raised, pale, translucent, blister-like pustules; leaves transmit light when held up; plant glabrous………E. leptocephala
1  Leaves without pale pustules, or if present then leaves opaque and do not transmit light; plants glabrate to pubescent.

Glabrous is smooth, glabrate means “almost smooth”, and a pubescent area is covered in short hairs.

closeup of stem and leaf base showing hairs

closeup of stem and leaf base showing hairs

 

Have a look at this photo. Clearly the plant is hairy, so I chose the second line, which leads to this couplet:

 

 

 

2  Major veins on leaf underside 3-5 (if 3 then all 3 veins bold), leaves 5-12 mm wide; heads with 20-50 flowers.
2  Major veins on leaf underside 1-3 (-5) (if 3 or 5 then only the midvein bold), leaves <6 mm wide (-8 mm wide in E. gymnospermoides); heads with 10-20 flowers.

leaf base, underside

underside of leaf at base

In the field I measured the largest leaves that were still intact on the plant. (All the lower, presumably largest, leaves had turned brown and curled up and many had fallen off.) Most of them were in the 7-8 mm range. Every leaf I examined had five veins, though some were pretty hard to see. Given these facts, I chose the first line of couplet 2 (more about the flower heads later), which leads to

3  Leaves 3-6 (-8) mm wide, punctae on leaf upperside bold, flower heads 10-20 flowered………..E. gymnospermoides
3  Leaves 5-12 mm wide, punctae on leaf upperside obscure or not bold, flower heads 20-50 flowered.

Again based on leaf width, and the fact that the punctae (dots) were not bold, I chose the second line, which leads to

4  Leaf undersides, upper stems, and branches glabrate, often with villous hairs on midrib of leaf underside …………………E. graminifolia var. graminifolia 
4 Leaf undersides, upper stems, and branches copiously to moderately short villous
…. E. graminifolia var. nuttallii

Look at the first picture again; I’d call that copiously villous. (“Villous” means covered in soft hairs.)

flower heads (7/32" long)

flower heads (7/32″ long)

About the flowers… Remember that plants in the Asteraceae have composite flowers. That little thing next to the ruler in this picture, measuring only about five and a half millimeters long, is a flower head – a collection of flowers. At least, it was, as these had all turned to seed. I was able to cut some open and tease out the seeds. I didn’t count more than 20 in any single head, which suggests about 20 flowers (each flower produces one seed). But, they were minute, and I was working with a small knife and a 10X hand lens, so it’s quite likely my count was inaccurate. Since I couldn’t get a true count of flowers per head, I ignored that part of the key.

seeds

seeds

So there it is. My mystery grass-leaved goldenrod/goldentop is Euthamia graminifolia var. nuttallii.

One thought on “Weakley Flora to the Rescue! (With a Primer on Using Botanical Keys)

  1. Pingback: Happy New Year! | Elizabeth's Wildflower Blog

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