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Published In: O Prirozenosti Rostlin 254. 1820. (Jan-Mar 1820) (Prir. Rostlin) Name publication detail
 

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ASTERACEAE (COMPOSITAE) (Sunflower Family)

Plants annual or perennial herbs (shrubs or less commonly trees), rarely scrambling or climbing. Stems branched or unbranched, rarely twining. Leaves alternate, opposite, or less commonly whorled, occasionally all or mostly basal, variously simple or compound, petiolate or sessile, rarely perfoliate, lacking stipules. Inflorescences terminal and/or axillary, composed of heads, these 1 to many per stem, sessile or stalked, solitary or more commonly in secondary inflorescences of clusters, spikes, racemes, or panicles. Heads composed of a flat to conical or rarely concave receptacle surrounded by an involucre of bracts and with few to many dense florets, these sessile or very short stalked on the receptacle, sometimes with subtending receptacular (chaffy) bracts or hairs. Involucral bracts few to many, of various shapes and sizes, arranged in 1 to several series, rarely the inner series fused into a tube or cup. Flowers within a head (collectively referred to as florets) all perfect or sometimes some or all pistillate or staminate (Missouri plants then completely or incompletely monoecious, elsewhere less commonly dioecious), epigynous, actinomorphic (disc florets) or zygomorphic (ray or ligulate florets). Calyx represented by a pappus of hairs, awns, and/or scales, this sometimes reduced to a low crown or lacking. Corollas (3–)5-lobed, the lobes sometimes difficult to interpret in ray and ligulate florets. Stamens (4)5, the filaments usually free but attached to the corolla tube, the anthers usually fused laterally into a tubular ring, dehiscing by vertical slits along the inner side. Pistil 1 per floret, composed of 2 fused carpels, but with only 1 locule and 1 ovule. Placentation basal. Style 1, forked toward the tip, each of the 2 branches with an elongate stigmatic band or pair of lines along the inner side toward the tip (the tip itself often nonstigmatic). Fruits achenes. About 1,535 genera, 23,000–32,000 species, cosmopolitan.

Specialists in the Asteraceae and Orchidaceae have competed for decades for the honor of claiming their group to be the largest family of flowering plants, but in recent years the orchidologists seem to be outpacing the asterologists in the race to describe new species. Regardless, the Asteraceae are one of the largest and most morphologically diverse plant families, found in nearly all habitats and having almost every type of growth form imaginable. Given its size, the family has only moderate economic importance. Numerous species are cultivated as ornamentals and specimen plants, but a number of other species are considered noxious weeds, both in agricultural areas and in natural plant communities. Although several species are used as foods and beverages, the composites overall are less important in this regard than some other relatively large families, such as the grasses and legumes. Sunflower (Helianthus annuus), which is grown for its edible seeds and the oil that they contain, has perhaps the greatest economic impact. Natural products produced by members of the family include pyrethrin insecticides (originally from Tanacetum), an alternative source of natural rubber (Parthenium), resins (several genera, but notably Grindelia), and various medicinal remedies. The windborne pollen grains of Ambrosia, Iva, and Xanthium are strong allergens, contributing heavily to the incidence of hay fever during the late summer and autumn.

The most distinctive feature of the family is the dense grouping of flowers (florets) into a head that functions much like an individual flower in most other plant families. Heads may contain from few to numerous florets. In a few genera, the head may contain only a single floret, and such reduced heads may even be grouped into secondary heads. The involucre associated with each head consists of bracts that are most often green and herbaceous, but they can be papery, leathery, or hardened (occasionally burlike) in a minority of genera. These involucral bracts may occur in a single series and be similar in shape and size, but more commonly they form 2 to several overlapping series, with the outermost bracts sometimes noticeably shorter or longer than the others. In a few groups, an inner series of bracts is fused into a cuplike or cylindrical structure, usually with shorter, free bracts below or outside these. The modified branch tip (receptacle) that forms the center of each head varies from elongate-cylindrical to cone-shaped in some of the coneflowers to hemispherical or nearly spherical in several genera, or strongly concave in a few species of cudweeds (Gamochaeta); however, in most species it is relatively flat to slightly convex (Pl. 289 e). Subtending each of the florets in some species is a scalelike bract (Pl. 289 a), in which case the receptacle is said to be chaffy (vs. naked). In a few groups, the floret bases are surrounded by short or long hairs. The bracts subtending individual florets are known as chaffy or receptacular bracts, in contrast to the involucral bracts that subtend an entire head. Chaffy bracts are scalelike and hard or papery in texture. In many cases, the best way to observe the shape of the receptacle and the presence of chaffy bracts is to section a head lengthwise (Pl. 289 e) and to examine the cut surface.

The florets themselves are quite variable and provide characters important in the delineation of tribes, genera, and species. Heads may contain all perfect florets, all staminate or pistillate florets, or a mixture of these types. In some species, some of the florets may be totally neutral, functioning only as a visual attractant to pollinators. When two different types of florets are present, these are usually distinguishable based on differences in size and shape of their component structures. Staminate florets almost always have a slender, nonfunctional ovary and may even produce a style that remains undivided at the tip. Pistillate florets do not produce staminodes.

In all Asteraceae, what one might think of as normal sepals are absent and instead the outermost floral whorl is known as a pappus. Most species have a pappus consisting of numerous capillary bristles (fine hairs), plumose (featherlike) bristles, 1 to several awns (stiff, stout, bristlelike structures visibly tapered from the base), few to several scales, or some combination of these structures. Rarely, the pappus is reduced to a low crown or rim of tissue or is totally absent.

The most visible floral variations are in the corolla are size and shape. Many members of the family produce actinomorphic florets referred to as disc florets. In these, the corolla is usually 5-lobed. It may be a slender tube (as in most thistles), or it may be shorter and differentiated into a narrow basal tube, expanded throat, and erect or spreading lobes. Occasionally, one of the sinuses between the lobes may be deeper than the others. Zygomorphic florets among Missouri genera occur in two distinct types. In the tribe Cichorieae, the florets of a head are all perfect and similar in size and shape, with a single long, strap-shaped lobe that usually has 5 teeth at the tip. Such ligulate florets are unique to this tribe. Ray florets, in contrast, occur in most other tribes and are always positioned along the periphery of a head that also contains a central group of disc florets. They may be pistillate (look for a divided style at flowering) or neutral. Heads with all-ligulate florets are referred to as ligulate, heads with only disc florets are called discoid, and heads with central disc florets and marginal ray florets are referred to as radiate.

Classification within the Asteraceae has remained controversial. Traditionally, the family was divided on a worldwide basis into two subfamilies, Lactucoideae (Liguliflorae) and Asteroideae (Tubuliflorae), with 13–19 total tribes mostly in the Asteroideae. Beginning in the 1970s, a lengthy series of studies by various authors based on different types of data began to dismantle the traditional approach, combining some tribes and segregating some genera into new tribes (for a review, see Bremer, 1994). Molecular studies of the family began with the work of Jansen and Palmer (1987), whose research suggested that the most primitive living Asteraceae were a small group of morphologically anomalous genera of shrubs growing in arid to seasonally dry portions of South America for which a third subfamilial name, Barnadesioideae, was proposed. Subsequent molecular and morphological analyses have broken up the traditional Lactucoideae (now called Cichorioideae) with its single tribe Cichorieae (sometimes referred to by the synonymous Lactuceae) into a series of groups recognized variously as tribes or subfamilies, none of which occur in Missouri except Cichorieae in the strict sense. These studies also have tended to group the traditional Vernonieae and Cynareae (now Cardueae) with the cichorioid groups. Perhaps the greatest disagreement over how many tribes to recognize has focused on the traditional tribes Eupatorieae, Helenieae, and Heliantheae, which various specialists have treated as a single tribe or a multitude, based primarily on molecular evidence (Baldwin et al., 2002). Different authors (Bremer, 1994; Panero and Funk, 2002) presently recognize 3–11 subfamilies and 17–35 total tribes worldwide. The classification of genera of Asteraceae into natural lineages is likely to continue to change as future research incorporates more species samples and additional data sets into the phylogenetic analyses.

The present treatment has borrowed shamelessly from the Flora of North America’s Asteraceae volumes (Flora of North America Editorial Committee, in press), which were under production at the time that the Missouri draft was being prepared. This classification is slightly more conservative than the last major familial summary (Bremer, 1994), wherein the authors of the chapter on Helenieae, Karis and Ryding, continued to accept this tribe while admitting that it was not a natural group. The present treatment does not, however, reflect the current trend toward recognition of many more tribal names to circumscribe all of the fully monophyletic lineages while also preserving all of the traditional tribal epithets (Baldwin et al., 2002; Panero and Funk, 2002). It has the practical advantages of deviating less from the traditional classification in Steyermark (1963) and that users of the present book will be able to locate general information on temperate North American composites more easily within the Flora of North America volumes. Also, many of the larger, traditional genera have been broken up and the tribal grouping accepted here continues to place the segregates relatively closely together in the work. Those interested in comparing the traditional tribal organization of Missouri Asteraceae in Steyermark’s (1963) treatment with that accepted here should note that: 1) Steyermark’s Inuleae have been split into three tribes, Gnaphalieae, Inuleae, and Plucheeae; 2) Cynareae are now known by the older name Cardueae; and 3) Steyermark’s Helenieae and Heliantheae are combined under the latter name.

Because the question of how many subfamilies should be formally recognized taxonomically remains controversial, it seems most useful to deal with the Missouri Asteraceae only at the tribal level. The following key to tribes of Missouri Asteraceae tends to favor relatively easily observed characters, but flowering heads must be present to determine most of the tribes. It draws inspiration mostly from keys in Steyermark (1963), Cronquist (1980), Gleason and Cronquist (1991), and Voss (1996).

 

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1 1. Florets all ligulate (zygomorphic, perfect, the corollas with the short tube split at the tip into an elongate, flattened, strap-shaped lobe, this usually 5-toothed at the tip); sap milky, usually white, less commonly tan or orange ... 4. CICHORIEAE, p. XXX

Cichorieae
2 1. Some or all of the florets discoid (more or less actinomorphic although sometimes elongate and slender, perfect or imperfect, the corollas with 5 shallow or less commonly deeper lobes), sometimes ray florets also present along the margin of the head (these zygomorphic, pistillate or functionally sterile, the corollas with the short tube split at the tip into a ligulate lobe, this sometimes with 2 or 3 teeth at the tip); sap clear, not appearing milky

3 2. Stems and/or leaves appearing spiny or prickly, sometimes only with spine-tipped teeth along the leaf margins ... 3. CARDUEAE, p. XXX

Cardueae
4 2. Stems and leaves not spiny or prickly, but sometimes with roughened texture or stiff, pustular-based hairs

5 3. Some or all of the heads with the involucre either burlike and enclosing the florets or having hooks, spines, and/or tubercles on the bracts (sometimes only at the bract tip)

6 4. At least some of the involucres burlike, enclosing the florets, the surface and/or tip of the bracts with hooked tubercles (Xanthium) ... 7. HELIANTHEAE, p. XXX

Heliantheae
7 4. Involucres not burlike, but some or all of the bracts with straight spines or tubercles at the tip

8 5. Pappus absent (do not confuse pappus with chaffy bracts) (Ambrosia) ... 7. HELIANTHEAE, p. XXX

Heliantheae
9 5. Pappus present on all or most of the florets ... 3. CARDUEAE, p. XXX

Cardueae
10 3. Heads with the involucre neither burlike nor bearing hooks or spines on the involucre (specimens with heads appearing immersed in cottony hairs should be keyed under this lead)

11 6. Receptacle with well-developed chaffy bracts or numerous conspicuous bristles subtending or intermixed with all or many of the florets (occasionally only produced toward the central portion or toward the margin of the receptacle)

12 7. Individual heads difficult to differentiate, grouped into a dense, more or less spherical, headlike cluster at each stem or branch tip, the entire mass obscured by dense, woolly hairs; true involucral bracts absent, each head merely with chaffy bracts (Diaperia) ... 6. GNAPHALIEAE, p. XXX

Gnaphalieae
13 7. Individual heads easily differentiated, not grouped into dense, spherical masses (but grouped into hemispherical, headlike clusters subtended by 3 leaflike bracts in Elephantopus [Vernonieae]), not obscured by woolly hairs; involucral bracts present and well developed around each head

14 8. Involucral bracts with a well-differentiated appendage at the tip, this flattened, abruptly different in color and/or texture from the basal portion of the bract, and often with long-fringed or bristly margins; anthers with the base prolonged into a pair of slender, elongate, tail-like lobes (Centaurea) ... 3. CARDUEAE, p. XXX

Cardueae
15 8. Involucral bracts not differentiated into a basal portion and a dissimilar apical appendage; anthers with the base truncate, rounded, or cordate with short, rounded lobes

16 9. Involucral bracts entirely dry and papery or scalelike, straw-colored to tan or brown, less commonly with a narrow, green central band or small apical region; style branches mostly lacking a well-defined, sterile apical portion beyond the stigmatic lines, often truncate and densely hairy at the tip ... 1. ANTHEMIDEAE, p. XXX

Anthemideae
17 9. Involucral bracts with a well-developed, green central portion (the green color sometimes partially masked by purplish pigments), with or without thinner membranous to papery margins; style branches mostly with a well-defined (but sometimes short), sterile apical portion beyond the stigmatic lines or bands, this variously shaped and sometimes densely hairy ... 7. HELIANTHEAE, p. XXX

Heliantheae
18 6. Receptacle naked, sometimes with minute, irregular or toothed ridges around the attachment points of the florets or occasionally with a few short, inconspicuous bristles or bracts toward the margin of the head

19 10. Pappus absent, a minute crown, or of 120 awns or scales, these uncommonly with 1 to several bristlelike tips

20 11. Disc florets with the corolla bright yellow to orangish yellow or orange

21 12. Involucral bracts entirely dry and papery or scalelike, straw-colored to tan or brown, less commonly with a narrow, green central band or small apical region; stem leaves alternate

22 13. Style branches mostly lacking a well-defined, sterile apical portion beyond the stigmatic lines, often truncate and densely hairy at the tip; leaf blades most commonly deeply lobed (unlobed in Achillea ptarmica and some Artemisia species, all of which are aromatic when bruised or crushed) ... 1. ANTHEMIDEAE, p. XXX

Anthemideae
23 13. Style branches with a well-defined, sterile apical portion beyond the stigmatic lines, this more or less elongate, usually densely and minutely hairy on the outer surface and glabrous on the inner surface; leaf blades unlobed, the margins entire or toothed; plants not aromatic when bruised or crushed ... 2. ASTEREAE, p. XXX

Astereae
24 12. Involucral bracts with a well-developed green central portion (the green color sometimes partially masked by purplish pigments), with or without thinner membranous to papery margins; stem leaves alternate or opposite (the leaves rarely all or mostly basal)

25 14. All of the leaves or at least those toward the stem base opposite or, if all alternate, then the stem leaves with the blades lobed or divided ... 7. HELIANTHEAE, p. XXX

Heliantheae
26 14. All of the leaves alternate and none of the stem leaves lobed or divided

27 15. Stems wingless (except in Boltonia decurrens, with white to pale pink ray corollas); ray florets absent or with the corolla white, pink, or yellow; style branches with a well-defined, sterile apical portion beyond the stigmatic lines, this more or less elongate, usually densely and minutely hairy on the outer surface and glabrous on the inner surface ... 2. ASTEREAE, p. XXX

Astereae
28 15. Stems appearing narrowly to broadly winged; ray florets with the corolla yellow (sometimes with reddish lines or reddish-tinged at the base); style branches lacking a well-defined, sterile apical portion beyond the stigmatic lines, more or less truncate and densely hairy at the tip (Helenium) ... 7. HELIANTHEAE, p. XXX

Heliantheae
29 11. Disc florets with the corolla white, pink, lavender, purple, or blue

30 16. Heads radiate (Helenium) ... 7. HELIANTHEAE, p. XXX

Heliantheae
31 16. Heads discoid

32 17. Primary heads grouped into hemispherical, headlike clusters subtended by an involucre of 3 leaflike bracts (Elephantopus) ... 11. VERNONIEAE, p. XXX

Vernonieae
33 17. Primary heads sometimes in clusters, but not aggregated into secondary heads subtended by an involucre of bracts

34 18. Stem leaves all or mostly opposite, the blade triangular-ovate to ovate (Ageratum) ... 5. EUPATORIEAE, p. XXX

Eupatorieae
35 18. Stem leaves alternate, the blades linear (Palafoxia) ... 7. HELIANTHEAE, p. XXX

Heliantheae
36 10. Pappus of (10)20 to numerous slender (capillary) bristles, occasionally also with an outer series of shorter scales

37 19. Heads radiate, the ray florets with the corolla well developed and showy

38 20. Involucre 2.02.5 cm long, 35 cm in diameter; anthers with the base prolonged into a pair of slender, elongate, tail-like lobes; style branches lacking a sterile tip, the stigmatic lines continuous around the rounded, more or less glabrous tip (Inula) ... 8. INULEAE, p. XXX

Inuleae
39 20. Involucre 0.31.5 cm long, 0.33.0 cm in diameter; anthers with the base truncate, rounded, or cordate with short, rounded lobes; style branches with or without a sterile tip, the stigmatic lines not continuous around the tip, this variously truncate to elongate and often minutely hairy

40 21. Involucral bracts in 29 unequal to subequal noticeably overlapping series; style branches with the sterile apical portion more or less elongate, usually densely and minutely hairy on the outer surface and glabrous on the inner surface ... 2. ASTEREAE, p. XXX

Astereae
41 21. Involucral bracts of a single series of bracts of similar size and length, these not or only slightly laterally overlapping, sometimes fused laterally, usually subtended by an outer series of fewer minute, slender, nonoverlapping bracts; style branches lacking a well-defined, sterile apical portion, the tip usually truncate and densely hairy ... 10. SENECIONEAE, p. XXX

Senecioneae
42 19. Heads discoid or apparently so, sometimes with pistillate marginal florets but these with relatively short corollas (shorter than to about as long as those of the other disc florets), sometimes completely or incompletely dioecious in Gnaphalieae, the staminate and pistillate flowers then with similar corollas

43 22. Involucral bracts white to straw-colored or purplish-tinged, sometimes pale greenish-tinged toward the base when young, this fading to white or tan as the head matures; corollas (except those of the innermost florets in Pluchea [Plucheeae]) slender and tubular, with minute, inconspicuous lobes (except sometimes in staminate florets of the dioecious Antennaria [Gnaphalieae], with spreading, slightly more conspicuous lobes)

44 23. Involucral bracts thin and papery throughout, dull or somewhat shiny, glabrous except for the dense, woolly hairs at the base, these partially or nearly completely obscuring the bracts; leaves with densely woolly pubescence, at least on the undersurface, sometimes also with stalked glands ... 6. GNAPHALIEAE, p. XXX

Gnaphalieae
45 23. Involucral bracts thin and papery above a thicker, herbaceous to leathery basal portion, minutely hairy and usually also glandular, but not woolly, the hairs not obscuring the bracts; leaves minutely hairy on the undersurface, also with sessile glands (Pluchea) ... 9. PLUCHEEAE, p. XXX

Plucheeae
46 22. Involucral bracts green, at least toward the tip or along the midnerve, sometimes partially purplish-tinged; corollas of all but the outermost florets (these relatively numerous in Pluchea [Plucheeae]) relatively showy, the tube more or less slender but flared or swollen toward the tip, with sometimes small but noticeable, spreading lobes

47 24. Disc florets with the corollas bright yellow

48 25. Involucral bracts in 29 unequal to subequal, noticeably overlapping series; style branches with the sterile apical portion more or less elongate, usually densely and minutely hairy on the outer surface and glabrous on the inner surface ... 2. ASTEREAE, p. XXX

Astereae
49 25. Involucral bracts of a single series of bracts of similar size and length, these not or only slightly laterally overlapping, sometimes fused laterally, usually subtended by an outer series of fewer minute, slender, nonoverlapping bracts; style branches lacking a well-defined, sterile apical portion, the tip usually truncate and densely hairy ... 10. SENECIONEAE, p. XXX

Senecioneae
50 24. Disc florets with the corollas white, pale cream-colored, pink, purple, or blue

51 26. Involucral bracts of a single series of bracts of similar size and length, these not or only slightly laterally overlapping, sometimes fused laterally, sometimes subtended by an outer series of fewer minute, slender, nonoverlapping bracts ... 10. SENECIONEAE, p. XXX

Senecioneae
52 26. Involucral bracts in 29 unequal to subequal, noticeably overlapping series

53 27. Stem leaves all or mostly opposite or whorled ... 5. EUPATORIEAE, p. XXX

Eupatorieae
54 27. Stem leaves alternate

55 28. Pappus of each disc floret double, of an inner series of numerous capillary bristles and an outer series of minute scales or bristles (Vernonia) ... 11. VERNONIEAE, p. XXX

Vernonieae
56 28. Pappus of each disc floret single, the bristles all similar in length

57 29. Inflorescences unbranched terminal spikes or spikelike racemes, sometimes leafy and the lowermost heads then appearing axillary (Liatris) ... 5. EUPATORIEAE, p. XXX

Eupatorieae
58 29. Inflorescences flat-topped, rounded or elongate panicles (in poorly developed plants sometimes nearly racemose or reduced to a few stalked clusters of heads), the branches sometimes appearing somewhat racemose

59 30. Involucre 1.54.0 mm long; most of the florets pistillate and with the corolla reduced to a minute flap or short fringe on 1 side of the tip of the slender tube, only the central florets of the head truly discoid (perfect and with actinomorphic corollas) (Conyza) ... 2. ASTEREAE, p. XXX

Astereae
60 30. Involucre 415 mm long; all of the florets perfect or most of the florets pistillate (only the inner florets perfect), but then with a slender, tubular corolla with 3 minute, equal lobes at the tip

61 31. Leaf blades linear to lanceolate or narrowly elliptic; pappus bristles plumose, not fused at the base, white to light tan; florets all discoid, perfect; plants not aromatic nor with a faint, sweet fragrance when bruised or crushed (Brickellia) ... 5. EUPATORIEAE, p. XXX

Eupatorieae
62 31. Leaf blades ovate to elliptic; pappus bristles minutely toothed or barbed, not plumose, fused into a ring at the base, usually pinkish-tinged; florets of 2 kinds, the innermost florets perfect and discoid, those of the outer several series pistillate, with a slender, tubular corolla with 3 minute, equal lobes at the tip; plants strongly aromatic with a camphorlike or musky odor when bruised or crushed (Pluchea) ... 9. PLUCHEEAE, p. XXX Plucheeae
 

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