Flora of North America species comparison

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Ageratum houstonianum

Ageratum maritimum

bluemink, floss flower, Houston's whiteweed

Cape sable whiteweed
Habit Annuals, 30–80 cm (fibrous-rooted). Annuals or perennials, 10–50 cm (semisucculent, rhizomatous, forming colonies).
Stems

erect to decumbent, sparsely to densely pilose.

decumbent to straggling or creeping (rooting at nodes), glabrous but for puberulous-pilose nodes.
Leaf

blades deltate to ovate, mostly 3–8 × 2.5–4 cm, margins toothed, abaxial faces sparsely to densely pilose, not evidently gland-dotted.

blades deltate-ovate to oblong, mostly 0.8–4 × 0.5–3 cm, (fleshy) margins toothed, faces glabrous or glabrate.
Peduncles

viscid-puberulent, pilose, and stipitate-glandular.

glabrous or glabrate.
Involucres

ca. 4 × 5–6 mm.

ca. 3 × 3–4 mm.
Corollas

usually lavender, rarely white.

lavender or blue to white.
Phyllaries

narrowly lanceolate (0.6–1 mm wide), stipitate-glandular, sparsely to densely pilose, eciliate or inconspicuously ciliate, tips gradually tapering, indurate-subulate, 0.8–2 mm.

elliptic-lanceolate, glabrous or glabrate, tips abruptly tapered to nearly obtuse.
Cypselae

sparsely strigoso-hispidulous;

pappi of 5 distinct, oblong scales 2–3 mm.

glabrous;

pappi usually blunt coronas ca. 0.1 mm, rarely of separate scales.
2n

= 20.

Ageratum houstonianum

Ageratum maritimum
Phenology Flowering Jun–Aug. Flowering year round.
Habitat Disturbed sites, mostly coastal Beach sand and nearby thickets, coral soils, salt marshes, hammocks, roadsides
Elevation 0–20 m (0–100 ft) 0–10 m (0–0 ft)
Distribution
from FNA
AL; CT; FL; GA; MA; NC; SC; TX; Mexico; Central America [Introduced in North America; introduced, Pacific Islands (Hawaii)]
[WildflowerSearch map]
[BONAP county map]
from FNA
FL; Mexico (Quintana Roo); West Indies (Cuba, Hispaniola); Central America (Belize)
[BONAP county map]
Discussion

Ageratum houstonianum is apparently native to southeastern Mexico and Central America; the North American plants are escapes and naturalized from cultivars. M. F. Johnson (1971) observed that forma isochroum (B. L. Robinson) M. F. Johnson (type from the state of Veracruz, Mexico) sometimes may be nearly eglandular.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Plants from Florida (Ageratum littorale, the type from Florida) are described here. Plants of the West Indies and Mexico (broadening the species concept to A. maritimum, the type from Cuba) have various elaborations of vestiture and a more conspicuous pappus–coronas with even to laciniate margins or rings of nearly separate scales mostly 0.2–1.5 mm. In addition to the distinctive relatively small, glabrous or glabrate leaves, plants of A. maritimum are characterized by heads in clusters, usually held well beyond the leaves.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 21, p. 483. FNA vol. 21, p. 482.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratum Asteraceae > tribe Eupatorieae > Ageratum
Sibling taxa
A. conyzoides, A. corymbosum, A. maritimum
A. conyzoides, A. corymbosum, A. houstonianum
Synonyms A. conyzoides var. mexicanum A. littorale, A. littorale var. hondurense
Name authority Miller: Gard. Dict. ed. 8, Ageratum no. 2. (1768) Kunth: in A. von Humboldt et al., Nov. Gen. Sp. 4(fol.): 117. (1818)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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