Salix_petiolaris

Salix petiolaris

Important Synonyms:
Common Names: slender willow, meadow willow

General Remarks
S. petiolaris is now attributed to the Section Geyerianae together with two other willows from western North America: S. geyeriana and S. lemmonii. It was once placed together with S. sericea (another willow common in New England) in the section Griseae. By its vegetative characters, S. petiolaris is indeed very similar to S. sericea, so that these two species may be confused. S. petiolaris and S. sericea are quite similar not only morphologically, but also ecologically. They occupy almost the same niche: both are typical wetland plants. (Yet, differently from S. petiolaris, S. sericea do not avoid alluvial situations, i.e., may occur near running water.)
Differently from S. sericea, S. petiolaris reaches far to western North America, though not quite to the Pacific Ocean. In New England, this is a northern species. Although it is recorded from all of New England states and nearly all counties in Massachusetts (except for only DU, Martha's Vineyard), it occurs more rarely in southeastern Massachusetts, and farther toward the southern extremities of its range, in Connecticut and Pennsylvania, it becomes a species of Special Concern. It is possible that S. petiolaris, differently from S. sericea, avoids sandy soil. If we accumulate enough observations justifying this assumption, then we may provide in the future an additional explanation of this species' rarity in southeastern Massachusetts.

Description
Shrub to 6 m tall [1] [2] [3], stems erect; branchlets flexible at base, puberulent to glabrescent, yellow-green to red-brown. Leaves with stomata beneath (hypostomatous). Leaf blade 5-9 times as long as wide, base cuneate (with straight sides) or convex, margins flat to slightly curved under (revolute), entire, serrulate, or serrate; apex acute to acuminate, lower (abaxial) surface glaucous, densely silky-sericeous in spring [4] [5], later in season glabrescent to glabrous, hairs straight, white or white with some rusty (ferrugineous); upper (adaxial) surface dull or shiny, glabrous or sparsely pubescent, hairs white or white and ferrugineous [6]. Stipules rudimentary or absent; petiole shallowly grooved, 3-11 mm long, pubescent or velvety to glabrescent; not glandular at junction with leaf blade. Bark on stem and older twigs gray, cracked [7].
Catkins flowering as leaves emerge or just prior to that (coetaneous). Staminate catkins stout, subglobose or globose, densely flowered, 10-35 mm, flowering branchlets up to 4 mm [8]. Pistillate loosely flowered, 12-39 × 6-18 mm, flowering branchlets up to 11 mm [9], [10]. Staminate flowers: floral bracts tawny, light rose, brown, or bicolor, 1-2 mm, hairs on bracts white, straight; bract apex rounded, entire; stamens 2; anthers purple, becoming yellow; filaments hairy at base; nectary square, ovate, or oblong, 0.3-0.7 mm. Pistillate flowers: ovary pyriform (pear-shaped), sparsely short-silky; stipes 1.5-4 mm; nectary ovate or oblong, 0.3-0.9 mm, shorter than stipes; capsules 5-9 mm; styles 0-0.5 mm; stigmas slender-cylindrical.

Recognition
Coarse shrub with narrow leaves (5-9 times as long as wide), serrulate at margin, more or less glabrous or silky sericeous when young, with white and usually at least some rusty (ferrugineous) hairs; stipules absent or rudimentary. Catkins on leafy flowering branchlets; female (pistilate) catkins loose due to long fruit stipes, especially when ripe (ca. 10 times as long as nectaries). By the latter character, it resembles S. bebbiana, which also has loose catkins; however, these two willows have very different leaf shapes, serration, and venation (S. petiolaris leaves are not reticulate beneath).
S. petiolaris differs from S. sericea in flexible (not brittle) branchlets, on average narrower leaves, presence of rusty (ferrugineous) hairs on leaves, loosely flowered pistillate catkins (with long stipes), and pyriform (pear-shaped) ovaries with beaks gradually tapering to distinct style. Winter buds are also different in these two species. In S. petiolaris bud scale dies in winter, becoming dark or reddish-black; floriferous buds with a distinct beak [11], [12].

Habitat
Wetland Delineation Code: FACW or OBL. S. petiolaris occurs in swamps, fens, marshes, moist meadows (esp. sedge meadows), swales, wet shrub thickets, at openings in wet woods, and on pond shores.

Sources and References
1. Argus G.W. 1986. The genus Salix (Salicaceae) in the Southeastern United States. Systematic Botany Monographs 9. 170 pp.
2. Argus G.W. 2006. Guide to the Identification of Salix (Willow) in Illinois, Indiana, Ohio, and Pennsylvania. [https://www.researchgate.net/publication ...]
3. Argus G.W. 2008. A Guide to the identification of Salix (willows) in Alberta. [http://accs.uaa.alaska.edu/files/botany/ ...]
4. Argus G.W. 2010. Salix L. in Flora of North America North of Mexico, Volume 7. Magnoliophyta: Salicaceae to Brassicaceae, pages 23-162. Eds. Flora of North America Editorial Committee. Oxford and New York: Oxford University Press. Online version: [http://www.efloras.org/florataxon.aspx?f ...]


Last time modified 2016-04-26T10:19:43-07:00 (A.Zinovjev & I.Kadis)