This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
Flower-heads - Showy golden yellow, 1 to 2 1/2 in. across, numerous, on short peduncles; 8 to 10 neutral rays around a dingy yellowish or brown disk of tubular, perfect, fertile florets. Stem.: 1 to 2 ft. high. Leaves: Opposite, sessile, lance-shaped, regularly saw-toothed.
Flowering Season - August - November.
Distribution - Quebec and Minnesota, southward to the Gulf States and Lower California.
Next of kin to the golden coreopsis, it behooves some of the bur-marigolds to redeem their clan's reputation for ugliness; and certainly the brook sunflower is a not unworthy relative. How gay the ditches and low meadows are with its bright, generous bloom in late summer, and until even the golden-rod wands turn brown! Yet all this show is expended merely for advertising purposes. The golden ray florets, sacrificing their fertility to the general welfare of the cooperative community, which each flower-head is in reality, have grown conspicuous to attract bees and wasps, butterflies, flies, and some beetles to the dingy mass of tubular florets in the centre, in which nectar is concealed, while pollen is exposed for the visitors to transfer as they crawl. The rays simply make a show; within the minute, insignificant looking tubes is transacted the important business of life.
Bur-Marigold, Or Brook Sunflower (Bidens laevis)
Later in the season, when the bur-marigolds are transformed into armories bristling with rusty, two-pronged, and finely-barbed pitchforks (Bidens = two teeth), our real quarrel with the tribe begins. The innocent passerby - man, woman, or child, woolly sheep, cattle with switching tails, hairy dogs or foxes, indeed, any creature within reach of the vicious grappling-hooks - must transport them on his clothing; for it is thus that these tramps have planned to get away from the parent plant in the hope of being picked off, and the seeds dropped in fresh colonizing ground; travelling in the disreputable company of their kinsmen the beggar-ticks and Spanish needles, the burdock burs, cleavers, agrimony, and tick-trefoils.
Beggar-ticks, Stick-tight, Rayless Marigold, Beggar-lice, Pitchforks, or Stick-seed (B. frondosa) sufficiently explains its justly defamed character in its popular names. Numerous dull, dark, tawny orange flower-heads without rays, or with insignifi-ant ones scarcely to be detected, and surrounded by taller leaflike bracts, add little to the beauty of the moist fields and roadsides where they rear themselves on long peduncles from July to October. The smooth, erect, branched, and often reddish, stem may be anywhere from two to nine feet tall. Usually the upper leaves are not divided, but the lower ones are pinnately compounded of three to five divisions, the segments lance-shaped or broader, and sharply toothed. As in all the bur-marigolds, we find each floret's calyx converted into a barbed implement - javelin, pitchfork, or halberd - for grappling the clothing of the first innocent victim unwittingly acting as a colonizing agent.