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Published In: Magazin für die Neuesten Entdeckungen in der Gesammten Naturkunde, Gesellschaft Naturforschender Freunde zu Berlin 1(4): 259–261. 1807. (Mag. Neuesten Entdeck. Gesammten Naturk. Ges. Naturf. Freunde Berlin) Name publication detail
 

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21. Grindelia Willd. (gumweed, gum plant)

Plants annual, biennial, or perennial herbs, usually with taproots. Stems 1 to several, erect or ascending, usually with few to several ascending branches toward the tip, with fine, longitudinal lines or grooves, glabrous or occasionally sparsely hairy toward the base (variously hairy elsewhere). Basal leaves absent at flowering, similar to the lower stem leaves, short- to long-petiolate. Stem leaves sometimes somewhat reduced toward the tip of the stem, sessile, the blade linear to narrowly oblong, oblong-lanceolate or oblong-obovate, rounded to bluntly or sharply pointed at the tip, tapered to rounded, truncate, or shallowly cordate at the usually slightly to strongly clasping or sheathing base, the margins entire or variously toothed (the lowermost leaves occasionally appearing somewhat lobed), the surfaces glabrous, with moderate to dense, impressed glandular dots. Inflorescences appearing as solitary heads or less commonly loose clusters at the branch tips, occasionally a few heads also in the axils of the adjacent leaves. Heads often relatively short-stalked, with few to several short, inconspicuous, linear bracts that grade into the involucral bracts, radiate or rarely discoid, slightly to strongly resinous-sticky. Involucre 6–15 mm long, cup-shaped to hemispherical or broadly urn-shaped, slightly to strongly resinous-sticky. Involucral bracts in 3–9 unequal to subequal, overlapping series, mostly narrowly lanceolate to linear, thick and yellowish below the midpoint, the tip green and usually with inrolled margins, loosely ascending to recurved or curled, the surface glabrous, with sparse to dense, impressed glandular dots. Receptacle flat or slightly convex, sometimes with low, toothlike ridges around the attachment points of the florets. Ray florets 14–45 or rarely absent, when present pistillate, the corolla 8–20 mm long, yellow, not persistent at fruiting. Disc florets numerous (more than 100), perfect or some of the outer or inner ones sometimes functionally staminate, the corolla 4–8 mm long, yellow, not persistent at fruiting. Pappus of the ray and disc florets similar, either of 2–8 awns or numerous bristles, in either case, these variously slightly shorter than to longer than the disc corollas, smooth or minutely barbed, off-white to straw-colored or light brown, not persistent or more or less persistent at fruiting. Fruits often of 2 types, those of the disc florets somewhat flattened, those of the ray florets more or less 3- or 4-angled in cross-section, both types more or less oblong to slightly wedge-shaped in outline, often more or less truncate at the tip (sometimes with the angles extended into minute teeth), the surface smooth or finely and inconspicuously few-nerved, glabrous. About 30–55 species, North America to South America, introduced in the Old World.

Grindelia was the subject of Julian Steyermark’s doctoral research, and his dissertation studies resulted in a lengthy series of papers on various aspects of the ecology, cytology, and systematics of the genus, including a taxonomic monograph of the North American species (Steyermark, 1934). A notable feature of gumweed species is their production of sticky, resinous exudates consisting mostly of complex mixtures of terpenes. These are produced by glands that are usually sunken into the surface of most of a plant’s tissues but are especially noticeable on the leaves and heads. Young heads often have the saucerlike space on top of the developing disc florets filled with a characteristic shiny layer of milky-white resin. Resin production in the genus has been studied for possible industrial applications as a substitute for conifer resins (Hoffmann et al., 1984). In particular, the Californian G. camporum Greene has been documented to produce resins at about 10 percent of the dry weight of the aboveground portion of the plant (McLaughlin, 1986; Hoffmann and McLaughlin, 1986), making it feasible for potential future development as an arid-adapted crop in the southwestern United States. This same resinous exudate had a long history of use among Native Americans for skin sores and lesions, to bind together edges of wounds, as an inhalant for bronchitis and asthma, and taken internally for coughs and a variety of other ailments (Steyermark, 1963; Moerman, 1998).

 

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1 1. Pappus of numerous bristles, these fused at the base, persistent or sometimes shed long after the fruit matures ... 1. G. CILIATA

Grindelia ciliata
2 1. Pappus of 2–8 slender awns, these not fused, usually shed as the fruit matures

3 2. Involucral bracts loosely ascending to slightly curved outward; leaves usually appearing only slightly resinous, the impressed glandular dots moderate to dense but inconspicuous and only slightly differing in color from the surrounding leaf tissue; margins of the leaves sharply toothed (rarely entire), the teeth mostly with a minute, bristlelike extension at the tip ... 2. G. LANCEOLATA

Grindelia lanceolata
4 2. Involucral bracts strongly curled or recurved; leaves usually appearing strongly resinous, the impressed glandular dots relatively dense and conspicuously darker than the surrounding leaf tissue; margins of the leaves rarely entire or nearly so, more commonly relatively bluntly toothed, the teeth usually with a thickened or glandular tip and lacking a spinelike or bristlelike extension ... 3. G. SQUARROSA Grindelia squarrosa
 
 
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