Following is Welsh's opening key to
Asteraceae (which he calls "Compositae"):

1. Corollas all raylike; plants usually with
milky juice....................................Key 1
-- Corollas not all raylike, some or all of
them tubular; juice seldom if ever milky..2
2(1). Corollas all tubular (discoid); no ray
flowers present, or the rays vestigial and minute.........................................Key 2
-- Corollas not all tubular;ray flowers present..............................................3
3(2). Pappus of capillary bristles, at least in part.............................................Key 3
-- Pappus of awns or scales, or lacking....4
4(3). Pappus lacking.......................Key 4
-- Pappus present, of awns or scales.Key 5

Workshop Part 1: Names   Workshop Part 2: Definitions and plant parts  Workshop Part 3: Keys   
Workshop Part 4: Keys
   Workshop Part 6: Keys and species

Part 5: Keys, C

 

Weber's Colorado Flora

Note the two family names.  Note also the amazing amount of information that Weber packs into a small space.

Arnica cordifolia

Arnica cordifolia, ARCO9

                                                              

 

Arnica cordifolia

Each grouping (1a/1b, 2a/2b, 3a/3b) is  called a couplet.  Note that the distinguishing characteristics in each couplet are physical features that we can observe:

Opposite vs. alternate leaves
Shape of phyllaries
Shape of flower head
Size of leaves
Type of root

  Terms to understand:
Ligulate, pappus, involucre, plumose, alternate/opposite, phyllaries, turbinate, rhizome, receptacle (the receptacle is what is left of the Dandelion after the silvery puff with seeds is gone).

    Arnica cordifolia, arco9
Complete description from A Utah Flora, 5th edition

Arnica cordifolia Hooker, Fl. Bor.-Amer. 1: 331. 1834.
[Type: alpine woods of the Rocky Mts., on the e. side, T. Drummond s.n.,
holotype K] Heartleaf arnica
Plants 1.5–4 dm tall, the stems erect or ascending, simple or branched
above, sparsely villous with multicellular hairs and often glandular as
well; basal leaves smaller than the cauline, often withered at anthesis;
petioles of main leaves (at least) often longer than the blades; cauline
leaves 2–4(5) pairs, the blades 2–9 cm long (from sinus to apex), 1–9 cm
wide, cordate-ovate to orbicular or reniform, or the uppermost lanceolate,
the largest below the middle of the stem, the lower leaves petiolate, the
upper ones sessile or subsessile, serrate-dentate to subentire; heads 1 (3),
rarely more, the peduncle apex villous with whitish hairs often intermixed
with glands; involucres 14–20 mm high, the bracts lanceolate to oblong,
acuminate to acute, sparsely to densely pilose and often glandular-ciliate,
the tip with a moderate tuft of hair; rays usually 10–15, yellow; achenes
4–5.5 mm long, uniformly hairy and often glandular; pappus white,
barbellate; n = 19, 38+.
1. Basal and lower cauline leaves commonly definitely cordate, the
blades mostly 4–12 cm long and 3–9 cm wide, commonly coarsely
toothed; plants common at lower middle to high elevations. . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . var. cordifolia
– Basal and lower cauline leaves scarcely or not at all cordate; the
blades mainly 2–5.5 cm long and 1.5–4 cm wide, commonly entire;
plants relatively rare at high elevations.. . . . . . . . . . . var. pumila
Var. cordifolia
Sagebrush, Douglas fir, white fir, lodgepole pine, ponderosa pine,
aspen, and spruce-fir communities at 1525 to 3355 m in Beaver, Box
Elder, Cache, Carbon, Daggett, Davis, Duchesne, Emery, Garfield, Grand,
Iron, Juab, Kane, Millard, Piute, Rich (KM 2005), Salt Lake, San Juan,
Sanpete, Sevier, Summit, Uintah, Utah, Wasatch, Washington, and Weber
cos. (lacking Morgan); Alaska to Michigan, s. to Calif., Ariz., N. Mex.,
and Nebraska; Parry 59, 1875 ISC-Parry!; 192 (xiii).
Var. pumila (Rydberg) Maguire, Madrono 6: 154. 1942.
[A. pumila Rydberg, Mem. N.Y. Bot. Gard. 1: 433. 1900; Type: Colorado,
Gray’s Peak, Torrey s.n., Aug. Sep. 1872, holotype NY]
Spruce-fir at or near timberline and alpine talus slopes at 2590 to 3570
m, in Cache (Naomi Peak), Duchesne ,Summit, and Uintah (Uinta Mts)
Piute (Tushar Mts.) San Juan (La Sal Mts.), Sevier (Fish Lake) cos.; Ore.,
Nev., and Colo.; 12 (0).
This variety is placed in synonymy of the species in FNA 21: 374. 2006.


 

 

Arnica L. 1753 means?

Fragrances are useful in identifying plants.  Arnicas often have a lemon fragrance.

Terms to understand:
Ray/disk, cauline, obtuse/acute, subplumose, barbellate, rosette, lanceolate, petiole, basal rosette, cordate, achene, apomictic, and the many terms that describe hairiness and hairs (trichomes): pubescent, puberulent, pustulose, tomentose, stellate, strigate, sericeous, hirsute, villous, pilose, glandular, glaucous. 

Apomictic (without mixing): producing seeds from unfertilized ovules.

These terms don't have to be memorized; refer to your flora's glossary.

Pappus

Pappus variations
A. pappus of simple bristles; B. beaked achene with pappus of plumose (feather-like) bristles; C. pappus of fringed scales; D. pappus of a crown of low scales (awns); E. pappus of deciduous or persistent scales with 2 more prominent than the others; F. pappus of backwardly barbed aristae (awns); G. achene without a pappus (epappose) and with a circular corona.
From Walters & Keil, 1975. 


Arnica cordifolia

Arnica mollis

Notice the differences in the pappus hairs: white barbellate bristles versus tawny subplumose bristles (Weber and Welsh) plumose (FNA).  Other pappus terms: capillary bristles, awns, scales.

Workshop Part 1: Names   Workshop Part 2: Definitions and plant parts   Workshop Part 3: Keys   
Workshop Part 4: Keys
   Workshop Part 6: Keys and species