Comprehensive DescriptionRead full entry
General: Sunflower Family (Asteraceae). Deciduous shrubs 1-2(-6) m tall, sometimes single-stemmed from the base and tree-like. Leaves: deciduous, obovate to elliptic or narrowly elliptic-oblanceolate, 3-nerved, 2-6 cm long, smooth-margined or with 1 tooth or 1-3 pairs of coarse teeth on the upper margins, the surfaces slightly resinous, usually with small dots. Florets closely clustered in heads surrounded by involucral bracts, the heads borne in tight aggregations; heads of two sexes, each produced on a separate plant (the species dioecious) –– the staminate heads (pollen-producing, with sterile ovaries) with only tubular, 5-lobed corollas; the pistillate heads (with fertile ovaries) with only thread-like corollas. Fruits (“cypselae” or achenes) are 1-seeded, nearly cylindric, 1.3-1.8 mm long, topped by a ring of numerous, slender, flexible, silvery-white bristles (the “pappus”), which elongates at achene maturity to 10-12 mm long, much longer than the involucre. The small fruits are shed with the pappus, a wind-catcher that enables fruit dispersal over a wide area. In a steady wind of about 17 km/hour, drift of seeds from a shrub two meters in height has been recorded up to 140 meters. The common name “silverling” alludes to the silvery aspect of pistillate plants in the fall, when the pappus of each maturing fruit elongates and protrudes from the head.
Variation within the species: Plants of this species from the West Indies have been called Baccharis halimifolia var. angustior DC., but there appears to be little justification for their formal recognition. Baccharis halimifolia closely resembles the Mexican species Baccharis heterophylla Kunth. Where both occur in Veracruz, Mexico, B. halimifolia can be recognized by its habitats along the coast or coastal plain, its more gradate, blunt-tipped involucral bracts, and its longer pappus. Plants from central Nuevo León, Mexico, have narrower leaves than typical for B. halimifolia, but in most respects they are more similar to it than to B. heterophylla. Baccharis halimifolia hybridizes with B. neglecta Britt. where the two meet in east Texas.
Groundsel tree is a member of the sunflower family, but the sunflower-like nature of the heads is not evident without close inspection. Baccharis halimifolia is the species upon which the concept of the genus Baccharis is based (the type species).