Salix subg. Protitea
Bot. Mag. (Tokyo) 42: 290. 1928.
Shrubs or trees, 1–30 m, not clonal, or clonal by stem fragmentation. Stems usually erect; branches flexible to highly brittle at base or throughout, glaucous or not. Buds alba-type, scale margins distinct, overlapping. Leaves: stipules on early ones usually rudimentary, sometimes absent or foliaceous, on late leaves foliaceous, rarely rudimentary (deciduous early or autumn); petiole usually deeply grooved adaxially (except S. floridana), not usually glandular distally (sometimes with basilaminar, spherical, or foliaceous glands); largest medial blade usually hypostomatous, sometimes amphistomatous, narrowly oblong, oblong, narrowly ovate, lorate, lanceolate, narrowly elliptic, or linear, 2.5–13 times as long as wide, angles of base and apex less than 90o, surface hairs usually white, sometimes also ferruginous; juvenile blade hairs white, sometimes also ferruginous. Catkins usually flowering as leaves emerge (sometimes throughout season, axillary, sessile in S. bonplandiana), from lateral buds; staminate from flowering branchlet, slender to stout; pistillate from flowering branchlet, usually loosely flowered, slender to stout; floral bract usually tawny, sometimes greenish, apex entire, erose, 2-fid, or irregularly toothed; pistillate bract deciduous (persistent in S. floridana, sometimes S. bonplandiana) after flowering. Staminate flowers: abaxial nectary present; stamens 3–7 [–9]; filaments usually distinct, sometimes connate less than 1/2 their lengths, usually hairy basally, sometimes on proximal 1/2; anthers yellow, usually globose. Pistillate flowers: abaxial nectary absent, (adaxial nectary shorter than stipe); ovary not glaucous, usually glabrous, sometimes villous, beak slightly bulged below or tapering to styles; ovules 4–24 per ovary; styles usually connate, sometimes distinct distally; stigmas usually flat, abaxially non-papillate, tip usually rounded, or stigmas slenderly cylindrical, or 2 plump lobes.
North America, Mexico, West Indies, Central America, Asia
Species 33 (7 species in the flora).
Two of the three sections recognized in this subgenus are found in the flora area.
Subgenus Protitea includes the New World members of sects. Floridanae and Humboldtianae. These sections often are placed in subg. Salix along with sect. Salicaster (R. D. Dorn 1976; G. W. Argus 1997; A. K. Skvortsov 1999); including them in a separate subgenus better emphasizes their position within the genus. Taxa in subg. Protitea are characterized by bud-scales with distinct, overlapping adaxial margins, flowers with 3–7[–9] stamens, and, usually, a tropical distribution. When subg. Protitea was described, it did not receive strong support. The debate was whether the multistaminate willows should be grouped on stamen number (T. Nakai 1928) or bud-scale characteristics (A. Kimura 1928). In a cladistic study of multistaminate Salix (Zhang M. L. 1994), members of subg. Protitea were in a clade that included two members of sect. Salicaster (subg. Salix). In a phenetic study of New World Salix (Argus), subg. Protitea appeared as a separate branch but was closely associated with a branch including members of subg. Salix. Two molecular studies provided equivocal results. A study based on ribosomal DNA (E. Leskinen and C. Alström-Rapaport 1999) included only one species from subg. Protitea (S. amygdaloides); it grouped with S. alba (subg. Salix). A study based on cpDNA, rbcL gene sequence (T. Azuma et al. 2000) placed members of subg. Protitea in a clade along with taxa from subg. Salix and subg. Longifoliae. Within this clade, species included here in subg. Protitea appeared on different branches. These results argue against the recognition of subg. Protitea but they were not definitive because the molecular cladistic studies included too few species of the subgenus and the morphological phenetic study did not account for polyploidy. All members of subg. Protitea for which we have counts are diploid; species in sect. Salicaster, the other section with multistaminate species, are polyploid. It is likely that sect. Salicaster, which is placed here in subg. Salix, originated through hybridization between members of subg. Protitea and subg. Salix followed by polyploidy. This would account for the occurrence of both multiple stamens and calyptrate bud-scales in the polyploid members of subg. Salix. Placing the diploid, multistaminate Salix with distinct, overlapping bud-scales in a subgenus separate from the polyploid, multistaminate Salix (sect. Salicaster) with calyptrate bud-scales would make subg. Protitea a more natural group. A study including a large sample of the 33 species in this subgenus would help resolve this question.
|1||Largest medial blades: abaxial surface not glaucous; pistillate bracts deciduous after flowering||> 2|
|1||Largest medial blades: abaxial surface glaucous; pistillate bracts deciduous or persistent after flowering||> 4|
|2||Largest medial blades usually linear, 10-28.6 times as long as wide, adaxial surface dull; stipules on late leaves usually rudimentary; ovaries with distinct, often raised veins||Salix humboldtiana|
|2||Largest medial blades narrowly elliptic or narrowly lanceolate, sometimes linear, 4.7-13.2 times as long as wide, adaxial surface slightly glossy; stipules on late leaves usually foliaceous; ovaries without distinct, raised veins||> 3|
|3||Branches red-brown to yellow-brown; capsules 3-5 mm; stipules on early leaves rudimentary or foliaceous, on late leaves usually foliaceous, apex usually acuminate or acute, glands few or absent adaxially; ovaries usually glabrous, rarely pilose; anthers with strongly recurved axes; branches highly brittle at base; pistillate adaxial nectaries oblong (swollen).||Salix nigra|
|3||Branches yellow-brown to gray-brown; capsules 6-7 mm; stipules on early leaves broad rudiments or foliaceous, on late leaves foliaceous, apex rounded to convex, glands numerous adaxially; ovaries usually glabrous, sometimes villous; anthers with straight axes; branches flexible to ± brittle at base; pistillate adaxial nectaries square (flattened).||Salix gooddingii|
|4||Pistillate bracts persistent after flowering||> 5|
|4||Pistillate bracts deciduous after flowering||> 6|
|5||Largest medial blades 38-55 mm wide, 2.5-4 times as long as wide, bases rounded to cordate, margins usually spinulose-serrulate, abaxial surface tomentose, adaxial highly glossy; petioles glandular-lobed distally; stipes 3.2-5.6 mm; styles 0.3-0.4 mm; Alabama, Florida, Georgia [2a1. Salix sect. Floridanae].||Salix floridana|
|5||Largest medial blades 7-27 mm wide, 4.5-10.7 times as long as wide, bases cuneate to convex, margins serrulate to crenulate, or entire, abaxial surface glabrous or glabrescent, adaxial dull or slightly glossy; petioles usually not glandular, rarely with spherical glands distally; stipes 0.4-2.4 mm; styles 0.2-0.3 mm; Arizona.||Salix bonplandiana|
|6||Branches, branchlets, petioles, and leaves glabrous; largest medial blades sometimes amphistomatous, adaxial surface dull; stigmas 0.24-0.4 mm.||Salix amygdaloides|
|6||Branches, branchlets, petioles, and leaves hairy, sometimes glabrate; largest medial blades hypostomatous, adaxial surface slightly to highly glossy; stigmas 0.16-0.28 mm||> 7|
|7||Largest medial blades: margins often entire, sometimes crenulate or serrulate; stipules rudimentary or foliaceous; floral bracts toothed; pistillate flowering branchlets 3-14 mm; stipes 1.4-2.8 mm; west of 102d meridian.||Salix laevigata|
|7||Largest medial blades: margins serrate or serrulate; stipules of late leaves foliaceous; floral bracts entire or erose; pistillate flowering branchlets 3-35 mm; stipes 1.3-5.3 mm; east of 102d meridian.||Salix caroliniana|