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Aquatic and Wetland Vascular Plants of the Northern Great Plains

Asteraceae - The Aster Family

Annual, biennial or perennial herbs (those included here) of various growth habits. Leaves simple or compound, exstipulate, opposite, alternate or both, sometimes whorled, occasionally the principal leaves basal. Flowers reduced in size, crowded into involucrate heads and sharing a common receptacle, the disk, the heads each resembling a single flower and arranged in various kinds of inflorescences; flowers of the head usually of 2 types, ray (or ligulate) florets simulating petals around the outside of the disk, and the usually less conspicuous disk (or tubular) florets occupying the central portion of the disk (to form a radiate head), or the head comprised entirely of ray florets (ligulate head), or disk florets (discoid head, Fig. 93c), the disk florets of a radiate or discoid head sometimes intermixed with bracts so that the receptacle is chaffy, otherwise the receptacle naked or pitted; involucral bracts sepaloid or foliaceous, surrounding and subtending the disk in 1-several series, often imbricate. Individual flowers perfect or imperfect*, regular (disk florets) or irregular (ray florets), lacking a definite calyx; a pappus of capillary bristles, scales or awns often encircling the summit of the ovary outside the corolla, commonly accrescent and persistent in fruit, often functioning in dispersal; corollas of 2 types, those of the ray florets tubular only at the base, expanded into the flat, petaloid ray or ligule, entire or toothed at the tip, the disk corollas tubular, with 5 equal lobes or teeth at the summit; stamens 5, epipetalous, usually with the elongate anthers united into a tube around the style; style branches usually 2, ovary inferior, 2-carpellary, 1-celled and 1-ovuled, ripening into an achene.

*Imperfect flowers in composite flower heads are commonplace. The ray florets of radiate heads are pistillate or sterile, whereas the disk florets are perfect or functionally staminate. In ligulate and discoid heads, usually all the florets are perfect, but in some discoid types, e.g., Xanthium, staminate and pistillate florets are borne in 2 very different types of discoid heads.

Lead Characteristic Go To
1 Heads ligulate, comprised entirely of yellow ray florets; plants with milky juice. Lead 2
1 Heads radiate or discoid; plants with watery juice. Lead 3
2 Leaves in a basal rosette like those of a dandelion; mature achenes terete. Genus Crepis
2 Leaves cauline; mature achenes flattened. Genus Sonchus
3 Leaves with sharp spines. Genus Cirsium
3 Leaves spineless. Lead 4
4 Leaves all opposite or whorled. Lead 5
4 Leaves alternate or partly so, or the leaves chiefly basal. Lead 8
5 Receptacle chaffy. Lead 6
5 Receptacle naked. Genus Eupatorium
6 Pappus none; leaves, or at least the upper ones, connate-perfoliate, forming a cup around the stem. Genus Silphium
6 Pappus of awns or awn-tipped scales; leaves sessile or petiolate, sometimes slightly connate, but not forming a cup around the stem. Lead 7
7 Pappus of 2-4 retrorsely barbed awns. Genus Bidens
7 Pappus of 2 awn-tipped scale. Genus Helianthus
8 Heads radiate with yellow rays. Lead 9
8 Heads discoid or radiate with rays colored other than yellow. Lead 13
9 Pappus of 2-several awns or scales. Lead 10
9 Pappus of numerous capillary bristles. Lead 11
10 Receptacle chaffy; leaves short-petioled, not decurrent on the stem. Genus Helianthus
10 Receptacle naked; leaves tapered to the base, decurrent as wings on the stem. Genus Helenium
11 Involucral bracts in one series, not imbricate, sometimes with a few reduced bracts below. Genus Senecio
11 Involucral bracts in few to several series, imbricate. Lead 12
12 Inflorescence corymbiform; leaves linear to linear-lanceolate or linear-elliptic, 2-10 mm wide, entire, glandular-punctate. Genus Euthamia
12 Inflorescence paniculiform; leaves lanceolate to elliptic, 10-40 mm wide, serrate, not glandular. Genus Solidago
13 Heads unisexual and dimorphic, the male florets in small heads above the larger female heads; involucres of the female heads spiny, completely enclosing the pistillate florets to form a bur. Genus Xanthium
13 Heads bisexual or rarely unisexual, all alike; involucres not spiny. Lead 14
14 Principal leaves basal, sagittate or palmate, white-woolly at least on the lower surface; flowering in spring or early summer. Genus Petasites
14 Principal leaves cauline, shaped other than sagittate or palmate, not white-woolly; flowering late summer or autumn (except Erigeron philadelphicus). Lead 15
15 Heads discoid. Lead 16
15 Heads radiate (the rays very narrow and only slightly, if at all, exceeding the involucre in Erigeron lonchophyllus and Conyza canadensis, therefore inconspicuous). Lead 18
16 Leaves pinnately dissected; pappus none. Genus Artemisia
16 Leaves simple, entire or toothed; pappus of numerous capillary bristles. Lead 17
17 Perennial with lanceolate to ovate-lanceolate leaves; involucral bracts purple-tipped. Genus Vernonia
17 Annual with linear leaves; involucral bracts green. Genus Aster
18 Pappus of 2 awns and several minute bristles. Genus Boltonia
18 Pappus of numerous capillary bristles. Lead 19
19 Plants taprooted annuals blooming in late summer or fall; involucre 3-4(5) mm high. Genus Conyza
19 Plants fibrous-rooted perennials, often with rhizomes, blooming in early or late summer or fall; involucre usually more than 4 mm high. Lead 20
20 Involucral bracts green, often chartaceous at the base; rays wider than 0.5 mm. Genus Aster
20 Involucral bracts hyaline at the tip and on the margins above, green in the middle and at the base; rays 0.1-0.6 mm wide. Genus Erigeron

Representative inflorescence types of the Asteraceae: a)radiate head, b)ligulate head, and c)discoid head.

49. Asteraceae, the Aster Family
1. Artemisia L. -- Sage, wormwood
1. Artemisia biennis Willd. -- Biennial wormwood
2. Aster L. -- Aster
1. Aster brachyactis Blake -- Rayless aster
2. Aster hesperius A. Gray -- Marsh aster
3. Aster junciformis Rydb. -- Rush aster
4. Aster lucidulus (A. Gray) Wieg.
5. Aster novae-angliae L. -- New England aster
6. Aster pauciflorus Nutt. -- Few-flowered aster
7. Aster praealtus Poir. -- Willowleaf aster
8. Aster pubentior Cronq.
9. Aster puniceus L. -- Swamp aster
10. Aster simplex Willd. -- Panicled aster
3. Bidens L. -- Beggarticks
1. Bidens bipinnata L. -- Spanish needles
2. Bidens cernua L. -- Nodding beggarticks
3. Bidens comosa (A. Gray) Wieg.
4. Bidens connata Muhl. ex Willd. -- Stick-tights
5. Bidens coronata (L.) Britt. -- Tickseed sunflower
6. Bidens frondosa L.
7. Bidens vulgata Greene
4. Boltonia L'Her -- Boltonia
1. Boltonia asteroides (L.) L'Her
5. Cirsium Mill. -- Thistle
1. Cirsium arvense (L.) Scop. -- Canada thistle
6. Conyza Less.
1. Conyza canadensis (L.) Cronq. -- Horseweed
7. Crepis L. -- Hawk's-beard
1. Crepis runcinata (James) T. & G.
8. Erigeron L. -- Fleabane
1. Erigeron lonchophyllus Hook
2. Erigeron philadelphicus L. -- Philadelphia fleabane
9. Eupatorium L.
1. Eupatorium maculatum L. -- Joe-Pye weed
2. Eupatorium perfoliatum L. -- Boneset
10. Euthamia Nutt.
1. Euthamia graminifolia (L.) Nutt. -- Narrow-leaved goldenrod
11. Helenium L. -- Sneezeweed
1. Helenium autumnale L.
12. Helianthus L. -- Sunflower
1. Helianthus grosseserratus Martens -- Sawtooth sunflower
2. Helianthus nuttallii T. & G. -- Nuttall's sunflower
13. Petasites Mill. -- Sweet coltsfoot
1. Petasites frigidus (L.) Fries
2. Petasites sagittatus (Pursh) A. Gray
14. Senecio L. -- Ragwort
1. Senecio congestus (R.Br.) DC. -- Swamp ragwort
2. Senecio pseudaureus Rydb.
15. Silphium L. -- Rosin-weed
1. Silphium perfoliatum L. -- Cup plant
16. Solidago L. -- Goldenrod
1. Solidago gigantea Ait. -- Late goldenrod
2. Solidago riddellii Frank -- Riddell's goldenrod
17. Sonchus L. -- Sow thistle
1. Sonchus arvensis L. -- Field sowthistle
18. Vernonia Schreb. -- Ironweed
1. Vernonia fasciculata Michx.
19. Xanthium L. -- Cocklebur
1. Xanthium strumarium L.

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