Jepson eFlora: Taxon page
Key to families | Table of families and genera
Previous taxon Index to accepted names and synonyms:
| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
Next taxon
Ambrosia trifida

Higher Taxonomy
Family: AsteraceaeView DescriptionDichotomous Key

Habit: Annual to tree. Leaf: basal and/or cauline, alternate, opposite, rarely whorled, simple to 2+ × compound. Inflorescence: 1° inflorescence a head, resembling a flower, of several types (see below), 1--many in generally +- cyme-like cluster; each head generally with +- calyx-like involucre of 1--many series of phyllaries (involucre bracts); receptacle of head flat to conic or columnar, paleate (bearing paleae = receptacle bracts) or epaleate; flowers 1--many per head. Flower: bisexual, unisexual, or sterile, +- small, of several types (see below); calyx 0 or modified into +- persistent pappus of bristles, scales, and/or awns; corolla radial or bilateral (0), lobes generally (0)3--5; stamens 4--5, filaments generally free, generally fused to corolla at tube/throat junction, anthers generally fused into cylinder around style, anther base generally rounded or cordate (deeply sagittate or with tail-like appendages), tip (= flattened appendage) generally projecting beyond pollen sac; pistil 1, 2-carpeled, ovary inferior, 1-chambered, 1-seeded, placenta basal, style 1, tip generally +- 2-branched (except in some staminate disk flowers), branch tips truncate or generally bearing +- brush-like appendages; stigmas 2, generally on adaxial faces of style branches. Fruit: achene (also called a cypsela) (drupe in Chrysanthemoides), cylindric to ovoid, sometimes compressed, generally deciduous with pappus attached.
Genera In Family: +- 1500 genera, 23000 species: worldwide, many habitats. Note: Flower and head types differ in form and sexual condition. A disk flower has a generally radial corolla, with a cylindric tube, expanded throat, and generally 5 lobes. Disk flowers are generally bisexual and fertile but occasionally staminate with reduced ovaries. Discoid heads comprise only disk flowers. A radiant head is a variant of a discoid head, with peripheral disk flower corollas expanded, often bilateral. A ray flower corolla is bilateral, generally with a slender tube and flattened petal-like ray (single lip composed of generally 3 lobes). Ray flowers are generally pistillate or sterile (occasionally lacking styles). Radiate heads have peripheral ray flowers and central disk flowers. Disciform heads superficially resemble discoid heads, with pistillate or sterile flowers that lack rays, together with or separate from disk flowers. A ligulate flower is bisexual, with a bilateral, generally ephemeral corolla and 5-lobed ligule. Liguliflorous heads comprise only ligulate flowers. See glossary p. 31 for illustrations of family characteristics. Echinops sphaerocephalus L., Gaillardia aristata Pursh, Gaillardia pulchella Foug., Hymenothrix loomisii S.F. Blake, Tagetes erecta L., Thelesperma megapotamicum (Spreng.) Kuntze are waifs. Melampodium perfoliatum Kunth, historic urban waif. Ageratum conyzoides L., Guizotia abyssinica (L. f.) Cass., Santolina chamaecyparisus L., orth. var. are rare or uncommon escapes from cultivation. Dyssodia papposa, Ismelia carinata (Schousb.) Sch. Bip. [Chrysanthemum carinatum Schousb.], Mantisalca salmantica (L.) Briq. & Cavill. are historical or extirpated waifs in California. Inula helenium L. not documented in California. Taxa of Aster in TJM (1993) treated here in Almutaster, Eucephalus, Eurybia, Ionactis, Oreostemma, Sericocarpus, Symphyotrichum; Chamomilla in Matricaria; Bahia in Hymenothrix; Cnicus in Centaurea; Conyza in Erigeron and Laennecia; Dugaldia in Hymenoxys; Erechtites in Senecio; Hymenoclea in Ambrosia; Lembertia in Monolopia; Osteospermum ecklonis in Dimorphotheca; Picris echioides in Helminthotheca; Prionopsis in Grindelia; Raillardiopsis in Anisocarpus and Carlquistia; Schkuhria multiflora in Picradeniopsis; Trimorpha in Erigeron; Venidium in Arctotis; Whitneya in Arnica. Amauriopsis in TJM2 (2012) treated here in Hymenothrix; Arida in Leucosyris; Bahia in Picradeniopsis.
Unabridged Note: Largest family of vascular plants in California and of eudicots globally.
eFlora Treatment Author: David J. Keil, except as noted
Scientific Editor: David J. Keil, Bruce G. Baldwin.
Genus: AmbrosiaView DescriptionDichotomous Key

Habit: Shrub to 15 dm; herbage +- thinly canescent-strigose. Stem: much-branched. Leaf: sessile or petiole to +- 1 cm; blade generally 1--2 × pinnately divided, abaxially strigose; lobes linear, inrolled margins forming densely hairy adaxial groove. Inflorescence: staminate and pistillate heads +- sessile, mixed in proximally leafy-bracted spike-like cluster; staminate heads 3--5 mm diam, phyllaries 5--6; pistillate heads 1-flowered. Fruit: bur +- 6 mm, fusiform, puberulent; wings 14--18, spiraled in several series, 3--3.5 mm, 1--1.75 mm wide, spine-tipped. Chromosomes: 2n=36.
Note: Sterile hybrid, Ambrosia dumosa × Ambrosia salsola; occasional where ranges of parents overlap.

Ambrosia trifida L.
Habit: Annual <= 2+ m, coarse. Stem: thick, fleshy, black-lined, soft-hairy to +- bristly; base +- woody. Leaf: generally opposite; petiole 1--5 cm; blade 6--35 cm, lanceolate to widely ovate, often palmately 3--5-lobed, serrate, short-rough-hairy. Inflorescence: staminate heads many in raceme-like clusters, 2--5 mm diam, phyllaries +- 10, 3 longest dark-lined; pistillate heads 1-flowered, clustered in distal leaf axils. Fruit: burs 6--12 mm, obovoid, green or straw-colored, glabrous or +- short-rough-hairy; spines 4--8, in distal ring around beak, 0.5--2 mm, conic, straight. Chromosomes: 2n=24.
Ecology: Dry, disturbed places; Elevation: < 800 m. Bioregional Distribution: n SnJV, CW, SW, MP; Distribution Outside California: native to central and eastern United States. Flowering Time: Jun--Sep Note: Occ, weed from bird seed, generally not long persisting in California.
eFlora Treatment Author: David J. Keil
Jepson Online Interchange
Noxious Weed

Previous taxon: Ambrosia salsola var. salsola
Next taxon: Amphipappus

Name Search


Citation for this treatment: David J. Keil Ambrosia trifida, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on November 19, 2017.

Citation for the whole project: Jepson Flora Project (eds.) 2017, Jepson eFlora,, accessed on November 19, 2017.

Ambrosia trifida var. trifida
click for enlargement
© 2016 Keir Morse
Ambrosia trifida var. trifida
click for enlargement
© 2016 Keir Morse
Ambrosia trifida var. trifida
click for enlargement
© 2016 Keir Morse
Ambrosia trifida
click for enlargement
© 2015 Barry Breckling
Ambrosia trifida var. trifida
click for enlargement
© 2016 Keir Morse
Ambrosia trifida var. trifida
click for enlargement
© 2016 Keir Morse

More photos of Ambrosia trifida in CalPhotos

Geographic subdivisions for Ambrosia trifida:
n SnJV, CW, SW, MP;
Markers link to CCH specimen records. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues. Purple markers indicate specimens collected from a garden, greenhouse, or other non-wild location.
map of distribution 1
(Note: any qualifiers in the taxon distribution description, such as 'northern', 'southern', 'adjacent' etc., are not reflected in the map above, and in some cases indication of a taxon in a subdivision is based on a single collection or author-verified occurence).

View elevation by latitude chart
Data provided by the participants of the Consortium of California Herbaria.
View all CCH records

CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.