Flora of North America species comparison

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Ageratum conyzoides

Ageratum houstonianum

tropical whiteweed

bluemink, floss flower, Houston's whiteweed
Habit Annuals, perennials, or sub-shrubs, 20–150 cm (fibrous-rooted). Annuals, 30–80 cm (fibrous-rooted).
Stems

erect, sparsely to densely villous.

erect to decumbent, sparsely to densely pilose.
Leaf

blades ovate to elliptic-oblong, 2–8 × 1–5 cm, margins toothed, abaxial faces sparsely pilose and gland-dotted.

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

minutely puberulent and sparsely to densely pilose, eglandular.

viscid-puberulent, pilose, and stipitate-glandular.
Involucres

3–3.5 × 4–5 mm.

ca. 4 × 5–6 mm.
Corollas

usually blue to lavender, sometimes white.

usually lavender, rarely white.
Phyllaries

oblong-lanceolate (0.8–1.2 mm wide), glabrous or sparsely pilose (margins often ciliate), eglandular, tips abruptly tapering, subulate, 0.5–1 mm.

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.
Cypselae

sparsely strigoso-hispidulous;

pappi usually of scales 0.5–1.5(–3) mm, sometimes with tapering setae, rarely 0.

sparsely strigoso-hispidulous;

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

= 20, 40.

= 20.

Ageratum conyzoides

Ageratum houstonianum
Phenology Flowering Jul–Aug. Flowering Jun–Aug.
Habitat Disturbed sites, mostly coastal Disturbed sites, mostly coastal
Elevation 0–20 m (0–100 ft) 0–20 m (0–100 ft)
Distribution
from FNA
AL; CA; CT; FL; GA; KY; MD; MO; MS; NC; HI; Central America; South America; West Indies [Introduced in North America; introduced, Mexico]
[BONAP county map]
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]
Discussion

Ageratum conyzoides is apparently native to South America. North American plants were escapes and naturalized from cultivation.

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

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.)
Source FNA vol. 21, p. 482. FNA vol. 21, p. 483.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratum Asteraceae > tribe Eupatorieae > Ageratum
Sibling taxa
A. corymbosum, A. houstonianum, A. maritimum
A. conyzoides, A. corymbosum, A. maritimum
Synonyms A. latifolium A. conyzoides var. mexicanum
Name authority Linnaeus: Sp. Pl. 2: 839. (1753) Miller: Gard. Dict. ed. 8, Ageratum no. 2. (1768)
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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