Identifying Asteraceae by using keys

I had hoped that learning tribes and subfamilies would help, but it really hasn't. Part of the problem is that the keys I have available are not set up in terms of tribes. The other is that whatever you do with these plants, you are going to have to start taking flowers (or inflorescences) apart and looking at little things with a hand lens, or better yet with a binocular microscope.

I am fortunate to have a binocular microscope at hand. This is a big improvement over a hand lens, not just for superior optics and lighting, but because you have both hands free to use tweezers or razor blades.

My approach to try to teach myself how to do this is to collect a number of plants I already know well and then key them out. This is working quite well.

Things you need

• A binocular microscope or hand lens.
• A key (flora) i.e. "Arizona Flora" in my area.
• Some fine tip tweezers.
• Some new sharp single edge razor blades
• A ruler graduated in mm and cm.
• A book to explain plant terms.

• How to identify plants

Asteraceae specific terms

• Head - a good word for a single inflorescence.
• Receptacle -- the thing the florets are "mounted" on -- is it bare or have scales, or bristles?
• Bracts on the Receptacle are palea, sometimes called "chaff scales" (these may come off with the flower, their presence or absence is important).
• The involucre of bracts below the flowers are the phyllaries
• Ray flowers are called "ligulate".
• Heads may be liguliforous (all ray flowers), or radiate (with peripheral ray flowers).
• A zygomorphic floret is a ray flower, an actinomorphic floret is a disc flower.
• The tube is the part of the corolla proximal to the stamen insertion.
• The limb is the part of the corolla distal to the stamen insertion. (proximal and distal are relative to the base of the flower.)
• What are commonly called achenes are actually cypselae.
• An achene is compressed if it has a long axis parallel to the head radius.
• An achene is dorsiventrally flattened if it has a short axis parallel to the head radius.
• Pappus -- bristles, hairs, or scales at the base of each floret, on top of the achene.
• Bristles and awns have near circular cross section.
• If it is flatter than 1:3 it is a scale.
• If it is less than 50 microns in diameter it is a fine bristle.
• If it is more than 100 microns in diameter it is an awn.
• A scale that ends in an awn is aristate.
• Pistil -- is it two forked, is it shaped like a baseball bat?
• Phyllaries -- how many rows are there?

Case studies

• Baileya multiradiata
• Cirsium wheeleri
• Achillea millefolium
• Hymenopappus filifolius
• Erigeron (2 species)
• Dieteria asteroides
• Rudbeckia laciniata

• unknown from behind Costco
• unknown from Rogers Rock

Artificial keys versus "Synoptical" keys

The "Manual of the Plants of Colorado" provides both sorts of key for the Asteraceae! That's the way to do things!

The California Jepson Manual uses an Artificial key, but a natural key has been published elsewhere (by Strother).

• JSTOR - link to Strother 1997

Here is the article abstract:

Synoptical keys are sometimes preferred to artificial keys. In the synoptical keys provided here, the 207 genera of composites recognized in The Jepson Manual represent 2 of the 3 subfamilies and 13 of the 16 tribes used in a classification system differing only slightly from that proposed by Bremer in 1994. Of the 207 genera treated in The Jepson Manual, Heliantheae (incl. Helenieae), as circumscribed here, includes 78 (distributed among 17 subtribes) and Astereae and Lactuceae have 33 each. The other ten tribes are represented in The Jepson Manual by 1 to 14 genera each.

Software driven keys

There are two flavors of these keys, MEKA (multiple entry key algorithm) and SLIKS. Actually SLIKS may simply be a public implementation of MEKA, but may require that the data be prepared in a certain way.

• SLIKS key software
• Jepson project MEKA keys
• SLIKS key for Asteraceae tribes
• JSTOR - link to Strother 1997