2a. Flowers more than 2 cm. long (5-10 dm. high) --3.
2b. Flowers about 1 cm. long, or shorter (flowers light blue) --4.
3a. Flowers scarlet =Cardinal Flower, Lobelia cardinalis.=
3b. Flowers blue =Great Lobelia, Lobelia siphilitica.=
4a. Flowers in loose racemes, pedicelled --5.
4b. Flowers in slender terminal spike-like racemes, nearly sessile (4-10 dm. high, usually unbranched) =Lobelia, Lobelia spicata.=
5a. Foliage p.u.b.escent (3-8 dm. high) =Indian Tobacco, Lobelia inflata.=
5b. Foliage glabrous (1-4 dm. high) =Lobelia, Lobelia kalmii.=
COMPOSITAE, the Composite Family
Herbs, with various types of foliage, but with flowers of characteristic structure, resembling a sunflower, a thistle, or a dandelion. Each apparent flower is a head of numerous small flowers, attached side by side to the expanded end of the stem, and subtended and partly enclosed by a series of bracts, called the involucre, which resembles a calyx.
The calyx of the individual flower is minute or actually wanting, and is usually modified to aid in seed dispersal. It appears at the base of the corolla, at the summit of the inferior ovary, and is known as pappus.
The structure of the pappus is best observed in the ripe fruit.
The corolla of the individual flowers consists of 5 (or rarely 4) united petals. In some flowers the petals are united to form a tubular or bell-shape corolla. In others they are united to form a flat or strap-shape corolla. The stamens are attached to the corolla, and are united by their anthers into a tube which surrounds the style, and above which the 2-lobed stigma protrudes.
The apparent flower of a Composite, composed of several or many individual flowers, is termed a head. It may be composed entirely of tubular flowers, as the thistle or bone-set; or entirely of strap-shape flowers, as the dandelion; or of both sorts together, as the aster or sunflower. In the latter case, the tubular flowers invariably occupy the center of the head, called the disk, and the larger strap-shape flowers are at the margin, where their projecting corollas, called rays, may be very conspicuous. Such heads are called radiate.
In a few composites (see 1a below) the flowers have minute corollas without colored parts.
In identifying a composite, determine first whether the heads are composed of tubular flowers, of strap-shape flowers, or of both sorts together; and, secondly, observe the nature of the pappus, using preferably the ripe heads, or at least the oldest flower-heads available. No further difficulties will be encountered.
1a. Flowers without petal-like or brightly colored parts; staminate and pistillate flowers in separate heads (or rarely in the same heads); coa.r.s.e weeds with inconspicuous flowers (summer and autumn) --2.
1b. Flowers with some petal-like parts, usually brightly colored or white --10.
2a. Leaves toothed or lobed --3.
2b. Leaves deeply pinnatifid or dissected (4-15 dm. high; flowers in erect spikes) (Ragweed) --7.
3a. Fruit or pistillate flowers thickly covered with sharp hooked spines (3-10 dm. high) (c.o.c.klebur) --4.
3b. Fruit not spiny --8.
4a. With spines on the stem at the base of the leaves =c.o.c.klebur, Xanthium spinosum.=
4b. Without any spines on the stem --5.
5a. Body of the bur smooth or slightly hairy =c.o.c.klebur, Xanthium canadense.=
5b. Body of the bur and the spines densely p.u.b.escent --6.
6a. Body of the bur more than twice as long as thick; a common weed =c.o.c.klebur, Xanthium commune.=
6b. Body of the bur less than twice as long as thick =c.o.c.klebur, Xanthium echinatum.=
7a. Leaves twice-pinnatifid =Ragweed, Ambrosia artemisiifolia.=
7b. Leaves once-pinnatifid =Ragweed, Ambrosia psilostachya.=
8a. Leaves deeply 3-lobed (1-5 m. high) =Giant Ragweed, Ambrosia trifida.=
8b. Leaves serrate or obscurely lobed --9.
9a. Stem simple or sparingly branched; pistillate heads in the axils of the upper leaves (1-3 m. high) =Giant Ragweed, Ambrosia trifida var. integrifolia.=
9b. Stem much branched; heads all alike, in panicles =Marsh Elder, Iva xanthifolia.=
10a. Flowers all strap-shape; juicy milky. (The central flowers must be examined carefully, since they are frequently much smaller than the marginal ones) --11.
10b. Flowers all tubular, with regular. 4-5-lobed corollas --45.
10c. Flowers both tubular and strap-shape; heads radiate (in a few species the rays are small and may be overlooked by mistake) --108.
11a. Flowers blue (summer and autumn) --12.
11b. Flowers orange, yellow, white, or purplish --15.
12a. Heads 2.5 cm. wide, or larger --13.
12b. Heads 1.5 cm. wide, or smaller --14.
13a. Leaves linear; bracts longer than the flowers, heads 5-10 cm. wide (6-15 dm. high) =Salsify, Tragopogon porrifolius.=
13b. Leaves broader, mostly serrate; bracts shorter than the flowers; heads 2.5-4 cm. wide =Chicory, Cichorium intybus.=
14a. Heads in a narrow crowded cl.u.s.ter (5-15 dm. high) --30b.
14b. Heads in a spreading open panicle (Wild Lettuce) --22.
15a. Heads solitary at the summit of leafless stalks --16.
15b. Heads several, on leafy, naked, or scaly stalks --19.
16a. Basal leaves strictly entire; heads about 2.5 cm. wide (summer and autumn) --35a.