fleabanes and horseweeds

genus Erigeron

Member of white daisies
sunflower family (family Asteraceae)
dicots (class Magnoliopsida)
flowering plants (subphylum Angiospermae)

Except for old historical records and extremely rare examples that I don't expect to encounter, there are no other wild species of this genus in the bay area.

Key features:

ray length (or not present)
disk corolla 4-lobed or 5-lobed
phyllarys graduated or ± equal
peduncle length
cauline leaf shape, clasping or not
basal leaves or not
leaf hair pattern (if any)
stem hairy or glabrous

heads with conspicuous rays

seaside daisy
Erigeron glaucus

rays 8–15 mm
leaves thick, ± fleshy, entire or toothed
all along Pacific coast (coastal bluffs, dunes, beaches)

leafy fleabane
Erigeron foliosus

rays 6–15 mm
phyllaries strongly graduated
no basal leaves
cauline leaves thread-like to widely oblanceolate, entire, not clasping, evenly sized and spaced
scattered
two variants distinguished by phyllary glands

mexican fleabane
Erigeron karvinskianus

ray 5–8 mm
phyllaries generally ± equal
no basal leaves at flower
cauline leaves elliptic to obovate, not at all clasping, entire or with 1–2 pairs of acute teeth or shallow lobes near tip
rare

philadelphia fleabane
Erigeron philadelphicus

rays 6–9 mm, very thin and extremely numerous
phyllaries generally ± equal
basal leaves present
cauline leaves clasping
uncommon

rays barely exceeding involucre

horseweed
Erigeron canadensis

rays 0.3–1 mm
central stem generally exceeding distal branches
heads ± short-peduncled in panicle-like clusters
leaf ± long-bristly-ciliate
central colored part of middle phyllaries narrower than light-colored margin, resin-filled, ± red-brown when dry
disk corolla generally 4-lobed
common

tropical horseweed
Erigeron sumatrensis

rays 0–0.3 mm
central stem generally exceeding branches
heads ± short-peduncled in panicle-like clusters
leaf margin ± fine-strigose
central part of middle phyllaries generally wider than lighter margin, not red-brown or resin-filled when dry
disk corolla generally 5-lobed
scattered mainly near Pacific coast

flax-leaved horseweed
Erigeron bonariensis

rays 0–0.3 mm
central stem often overtopped by distal branches in age
heads ± long-peduncled, generally in raceme-like clusters
leaf ± densely strigose and/or bristly
scattered

no rays

rock-loving fleabane
Erigeron petrophilus var. petrophilus

stem ± long-loose-spreading-hairy, densely glandular near heads or not
rare

narrow leaved rayless daisy
Erigeron reductus var. angustatus

stem glabrous
rare

5 observed taxons / 4 unobserved taxons / 1 key

Chris’s observations: 21 (14 are research grade)

Locations:

Kauai, HI: 4
Bear Creek Redwoods OSP: 3
Henry Cowell Redwoods SP - Fall Creek Unit: 2
Point Lobos SP: 2
Wilder Ranch SP: 2
Andrew Molera SP
Coyote Lake / Harvey Bear Ranch CP
DeLaveaga Park, Santa Cruz
Golden Gate National Recreation Area
Henry Coe SP
Murray Ranch SP
San Pedro Valley CP
Stevens Creek CP

Months:

Feb.: 1
Mar.: 0
Apr.: 1
May: 2
Jun.: 3
Jul.: 4
Aug.: 1
Sep.: 4
Oct.: 3
Nov.: 2

For more details, use advanced search.

Taxon info: iNaturalist – Calflora – Jepson eFlora – FNA

Bay Area species: iNaturalist – Calflora