Difference between revisions of "Geum"
Sp. Pl. 1: 500. 1753.
Gen. Pl. ed. 5, 220. 1754.
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Revision as of 20:38, 24 September 2019
Herbs, perennial, subscapose or leafy-stemmed, 1–12 dm, glabrous or hairy; from stout caudices or rhizomatous, fibrous-rooted. Stems 1–5, erect, simple. Leaves winter-persistent (basal), basal and cauline, simple, 3-foliolate, lyrate-pinnate, or odd-pinnate (commonly with smaller leaflets intermixed with larger ones); stipules often conspicuous, ± free or adnate to petiole or blade, linear, lanceolate, or ovate, margins entire, toothed, or lobed; petiole present, sometimes absent on cauline leaves; blade oblanceolate, obovate, elliptic, ovate, or orbiculate, herbaceous, major leaflets 1–26, rhombic, elliptic, oblong, obovate, oblanceolate, orbiculate, reniform, or cordate, margins flat, 2–7-lobed and/or laciniate, serrate, dentate, or crenate, venation pinnate or palmate. Inflorescences terminal, 1–18-flowered, cymes, open; bracts present as reduced cauline leaves; bracteoles present or absent. Pedicels present. Flowers 4–46 mm diam.; epicalyx bractlets, if present, 5 (10 in G. glaciale); hypanthium saucer-shaped to cup-shaped, 2–6 mm; sepals 5(–10 in G. glaciale), erect to erect-spreading, reflexed or not, deltate, deltate-ovate, or deltate-lanceolate; petals 5(–9 in G. glaciale), white to yellow, sometimes suffused with pink or purple, or purple-veined, obovate, orbiculate, ovate, obcordate, obdeltate, spatulate, suborbiculate, elliptic, or oblong; stamens [10–]25–120, shorter than petals; torus hemispheric to cylindric; carpels (2–)20–250(–450), styles entire or geniculate-jointed, distal portions then deciduous; ovule 1. Fruits aggregated achenes, (2–)20–250(–450), ovoid to fusiform, tapered apically into style, 2–4.5 mm; hypanthium persistent; sepals persistent, erect, spreading, recurved, or reflexed; styles persistent, becoming accrescent, hooked and elongating to 10 mm, or not hooked and elongating to 70 mm. x = 7.
Distribution
North America, Mexico, South America, Eurasia, Africa, Pacific Islands (New Zealand), Australia, temperate and arctic-alpine regions.
Discussion
Species ca. 45 (16 in the flora).
The most distinctive feature of many members of Geum is their geniculate-jointed style. The style has two parts, a persistent proximal segment and a deciduous distal segment. Where the two segments join, each bends to form a hook, with the hook of the proximal segment joined to the hook of the distal one. Seven of the 16 North American species of Geum lack this distinctive feature. Differences in style structure have led to differences in opinion as to generic delimitation and subgeneric classification of Geum.
During the early twentieth century, species traditionally included in Geum were divided among an increasing number of segregate genera. F. Bolle (1933), in his worldwide monograph, recognized five genera. After conducting extensive cytogenetic studies on Geum for two decades, W. Gajewski (1957) concluded that the most reasonable approach was to classify all the species in one genus. Most flora writers since Gajewski have maintained the species in a single heteromorphic genus. J. E. E. Smedmark and her collaborators have utilized DNA sequences from ITS, chloroplast trnL-trnF region, and nuclear low-copy gene GBSSI (Smedmark and T. Eriksson 2002; Smedmark et al. 2003), along with scanning electron microscopy of gynoecial development (Smedmark and Eriksson 2006), to test hypotheses by Gajewski of fruit evolution and allopolyploidy in Geum and to explore the phylogenetic relationships among the species. Their data support none of the previous circumscriptions of Geum as a monophyletic group, nor most of the suggested segregate genera favored by taxonomists such as Bolle, E. L. Greene (1906), and P. A. Rydberg (1913b). The taxonomic solution chosen here for North American species is traditional yet consistent with the molecular data and recognizes two genera: Geum for the polyploid (2n = 28–116), herbaceous species and Sieversia for the diploid (2n = 14), suffrutescent species. Smedmark (2006) found that Waldsteinia might best be treated within Geum. It is also possible that Coluria R. Brown, Taihangia T. T. Yu & C. L. Li, and Waldsteinia are sister to Geum (Smedmark and Eriksson 2002). Waldsteinia (2n = 14) is retained here as a separate genus, with its traditional circumscription.
Although most of Geum species in the flora area are reasonably distinct morphologically, their distinctive characteristics are not well correlated so as to be combined in a key using several characters per couplet, as was pointed out by E. G. Voss (1972–1996, vol. 2), whose key to Geum in Michigan served as a model for the key below. In particular, the characters that are useful in identifying specimens in flower do not correlate well with characters helpful in the identification of fruiting specimens. Specimens with both flowers and fruits are the easiest to identify with certainty, and both leads at couplet 11 in the key should be followed if possible. Petal color in Geum fades upon drying. Both white and yellow petals ultimately turn cream to pale yellow, thus rendering an important key character for fresh plants unreliable with most herbarium specimens. Collectors should note petal color on their labels.
For taxonomists familiar with Geum, leaves provide valuable characters for distinguishing the species, especially when flower color is not known. The complex morphology of leaves and their variability do not suit them for wide use in keys. Variability occurs both among plants of one species and on one plant. In many of the species with geniculate-jointed styles, the basal leaf form changes over the growing season. Spring-developing leaves are often pinnate followed by lyrate-pinnate or 3-foliolate leaves, and in late summer by simple leaves that are winter-persistent. For instance, the basal leaves of G. laciniatum may appear like those of typical G. aleppicum in late spring, but look more like those of G. macrophyllum var. macrophyllum in late summer. Cauline leaves may vary from pinnate proximally to 3-foliolate at mid stem to simple just proximal to the inflorescence. Because variability of leaves within a single species is nearly as great as between some species, leaf descriptions are kept short. Measurements of leaf length include the petiole, if present.
Selected References
Lower Taxa
Key
| 1 | Styles not geniculate-jointed, wholly persistent, 2–70 mm, apices not hooked (G. triflorum var. ciliatum often inconspicuously geniculate-jointed, distal segments tardily deciduous, remainder elongating at least 15 mm; G. schofieldii apices sometimes ± hooked); plants subscapose; stems 2–40(–60) cm; cauline leaves 0.7–5 cm, (not resembling basal) | > 2 |
| 1 | Styles geniculate-jointed, distal segments eventually deciduous, proximal segments persistent, 1.5–9 mm, apices hooked; plants leafy-stemmed; stems (20–)40–120 cm; cauline leaves (2–)5–23 cm, (proximal resembling basal, distal smaller) | > 8 |
| 2 | Basal leaves pinnate, terminal leaflets slightly larger than laterals | > 3 |
| 2 | Basal leaves lyrate-pinnate, sometimes simple, terminal leaflets larger than laterals | > 5 |
| 3 | Flowers nodding (erect in fruit); hypanthia maroon, purple, or greenish mottled with purple (may turn pale brown in fruit); petals erect, cream to yellowish suffused with pink or purple, or purple-veined; cauline leaves opposite. | Geum triflorum |
| 3 | Flowers erect; hypanthia green, or green and purple-tinged to strongly purple; petals spreading, yellow; cauline leaves alternate | > 4 |
| 4 | Stems densely pilose, hairs 2–5 mm; fruiting styles 18–30 mm, pilose except distal 1–3 mm. | Geum glaciale |
| 4 | Stems glabrous or downy, hairs to 1 mm; fruiting styles 2–5(–10) mm, glabrous throughout or pilose only at base. | Geum rossii |
| 5 | Basal leaves interruptedly lyrate-pinnate, major leaflets 5–7, interspersed with 2–8 minor ones. | Geum schofieldii |
| 5 | Basal leaves strongly lyrate-pinnate or simple, major leaflet 1, proximally 0–10 minor ones | > 6 |
| 6 | Stems densely hirsute proximally; inflorescences 3–10-flowered; pedicels glandular-hairy; fruiting styles glandular in basal 1/3. | Geum radiatum |
| 6 | Stems glabrate, sparsely downy, sparsely hirsute, or pilose proximally; inflorescences 1–2(–4)-flowered; pedicels downy and/or hirsute, usually eglandular; fruiting styles eglandular | > 7 |
| 7 | Cauline leaves 1.5–4.5 cm; fruiting styles 9–14 mm, pilose in basal 3/4; British Columbia, Alaska. | Geum calthifolium |
| 7 | Cauline leaves 0.8–1.7(–2.5) cm; fruiting styles 6–9 mm, pilose in basal 1/3; Nova Scotia, New Hampshire. | Geum peckii |
| 8 | Flowers nodding; sepals erect to erect-spreading, not reflexed; petals spatulate-obovate, apices rounded, truncate, or shallowly emarginate | > 9 |
| 8 | Flowers erect; sepals erect to spreading but soon reflexed; petals oblong, elliptic, suborbiculate, ovate, or obovate, apices obtuse to rounded | > 10 |
| 9 | Hypanthia greenish maroon to maroon; styles with distal segments 3–4.5 mm, shorter than mature proximal segments; fruiting tori on 4–10 mm stipes. | Geum rivale |
| 9 | Hypanthia green to greenish maroon; styles with distal segments 5–8 mm, longer than mature proximal segments; fruiting tori sessile. | Geum geniculatum |
| 10 | Fruiting tori on 3–7 mm stipes; epicalyx bractlets absent; sepals 1–3 mm; petals 1–2 mm. | Geum vernum |
| 10 | Fruiting tori sessile or on less than 3 mm stipes; epicalyx bractlets usually present (often absent in G. macrophyllum); sepals (2–)3–10 mm; petals 2–9 mm (rarely 1.5 mm in G. virginianum) | > 11 |
| 11 | Plants with flowers | > 12 |
| 11 | Plants with fruits | > 17 |
| 12 | Petals white or cream | > 13 |
| 12 | Petals yellow | > 15 |
| 13 | Petals (3–)4–8 mm, ± equal to or longer than sepals; stems glabrate to downy, hairs to 1.5 mm. | Geum canadense |
| 13 | Petals (1.5–)2–5 mm, shorter than sepals; stems hirsute or puberulent and hirsute to densely hirsute, some hairs 2–2.5 mm | > 14 |
| 14 | Pedicels puberulent, densely hirsute; cauline leaves with stipules 4–14 mm. | Geum laciniatum |
| 14 | Pedicels puberulent (sometimes with scattered hairs); cauline leaves with stipules 11–48 mm. | Geum virginianum |
| 15 | Styles with distal segments glabrous or with short hairs, hairs shorter than diam. of style; cauline leaves with stipules 10–40 × 5–35 mm. | Geum urbanum |
| 15 | Styles with distal segments pilose at base, hairs much longer than diam. of style; cauline leaves with stipules 7–28 × 3–22 mm | > 16 |
| 16 | Epicalyx bractlets often absent; styles with proximal segments sparsely to densely stipitate-glandular; basal leaves interruptedly lyrate-pinnate, terminal leaflets usually much larger than laterals. | Geum macrophyllum |
| 16 | Epicalyx bractlets present; styles with proximal segments eglandular; basal leaves interruptedly pinnate, terminal leaflets usually only slightly larger than laterals. | Geum aleppicum |
| 17 | Fruiting tori glabrous, puberulent, or with ring of bristles at base and tuft at apex | > 18 |
| 17 | Fruiting tori densely downy or bristly | > 19 |
| 18 | Fruiting styles with proximal segments sparsely to densely stipitate-glandular; epicalyx bractlets often absent; pedicels densely puberulent (sometimes with scattered longer hairs), sometimes stipitate-glandular. | Geum macrophyllum |
| 18 | Fruiting styles with proximal segments glabrous, sometimes 1–2 eglandular bristles at base; epicalyx bractlets present; pedicels densely puberulent, hirsute, eglandular. | Geum laciniatum |
| 19 | Fruiting styles with proximal segments with bristles on basal 1/3; fruiting tori densely downy (hairs soft, 0.3–0.7 mm); proximal cauline leaves mostly pinnately compound. | Geum aleppicum |
| 19 | Fruiting styles with proximal segments glabrous or glabrate, sometimes sparsely hairy or stipitate-glandular in G. canadense; fruiting tori densely bristly (hairs 1–2.3 mm); proximal cauline leaves usually 3-foliolate or simple and 3-lobed to unlobed, sometimes pinnate in G. urbanum | > 20 |
| 20 | Fruiting styles with distal segments glabrous or with short hairs, hairs shorter than diam. of style. | Geum urbanum |
| 20 | Fruiting styles with distal segments pilose in basal 1/2, hairs much longer than diam. of style | > 21 |
| 21 | Cauline leaves with stipules 4–13 × 1–7 mm; stems glabrate to downy. | Geum canadense |
| 21 | Cauline leaves with stipules 11–48 × 6–35 mm; stems puberulent and hirsute to densely hirsute. | Geum virginianum |