Philadelphus microphyllus
Philadelphus microphyllus var. microphyllus
little leaf mock orange, small-leaf mock orange
copper to reddish brown, stiffly to loosely branched, appressed villous-sericeous, ± strigose, hairs often red-gland based, or glabrous;
epidermis soon or tardily deciduous exposing cortex and striate bundle caps;
bark grayish;
internodes (0.1–)1–2.5(–6) cm; short-shoot spurs not present;
axillary buds hidden in pouches.
petiole 1–2(–4) mm;
blade greenish or whitish abaxially, green adaxially, linear-lanceolate, narrowly ovate to ovate, (0.5–)0.8–3(–5.5) × (0.2–)0.3–1.3(–3.3) cm, herbaceous to coriaceous, margins usually entire, rarely sparsely serrulate, plane or revolute upon drying, abaxial surface short sericeous-strigose, or sericeous-villous with longer hairs, or with ascending to erect hairs, sometimes with dense to moderate understory of slender curled hairs, adaxial surface glabrous, glabrate, ± sericeous-strigose, villous, or with erect hairs.
blades (0.8–)1–2.2(–4) × (0.3–)0.4–1(–1.8) cm, herbaceous to coriaceous, margins entire, abaxial surface gray-white, often mottled with brown, sparsely to moderately sericeous-strigose, hairs appressed or loosely appressed, 0.2–0.6 mm, or coarser, to 0.5–1.2 mm, or when vestiture dense, with understory of slender, wavy-curved hairs, or chaotically hirsute-pilose (through introgression with var. argyrocalyx), marginal hairs often more erect, adaxial surface green, drying dark brown (cuticle thin, finely papillate), mosaic of dark brown and yellowish gray-green (cuticle forming mosaic of thin, papillate areas and thick, smooth areas), or rarely uniformly yellowish gray-green (cuticle thick, smooth), usually sparsely sericeous-strigose, hairs appressed or slightly ascending, slender, 0.3–0.7 mm, sometimes glabrate or glabrous, rarely weakly hirtellous or with some erect hairs near base.
usually solitary flowers, sometimes 3–5-flowered cymes.
1(–3)-flowered.
0.5–3 mm.
hypanthium glabrous, sericeous-strigose basally or throughout, or weakly to densely villous to densely lanate with mixed strigose and villous vestiture, with understory of slender curled hairs;
sepals ovate to lanceolate, (2.5–)4–8.5(–10) × (2.5–)3–4.3(–5) mm, apex acute to acuminate-caudate, abaxial surface glabrous, sericeous-strigose, or weakly to densely villous to densely lanate with mixed strigose and villous vestiture, with understory of slender curled hairs, adaxial surface glabrous except villous along distal margins;
petals white [marked purple near base], oblong-obovate to broadly ovate, (5.8–)7–16(–21) × (5.3–)6–11(–15) mm, margins entire or erose-undulate, apex ± acute, rounded, or notched;
stamens 26–64;
filaments often connivent-connate in irregular clusters in proximal 0.5–4 mm, 1.8–8 mm, of unequal length, glabrous;
anthers yellowish, 0.7–1.2 mm;
styles 4, connate proximally, cylindric, 2.5–5.5(–7) mm, lobes sometimes connate proximally in pairs, 0.5–2.5 mm;
stigmatic surfaces extending from adaxial lobes onto abaxial lobes and down to cylindric style.
14–32 mm diam.;
hypanthium and sepal abaxial surfaces glabrous, sparsely sericeous proximally or in 4 lines extending from pedicels to alternate sepals, or moderately sericeous throughout, hairs appressed, coarse to fine, not obscuring epidermis, or densely sericeous-strigose with understory of thinner curved-wavy hairs completely obscuring epidermis;
sepals (3.5–)6.5–8 mm;
petals (5.8–)8–10(–15) × (5.3–)6–8(–10) mm;
stamens (26–)34–46.
oblong-globose or globose-turbinate, (3.6–)5–8(–9.5) × (3.5–)4–7(–9.5) mm, sepals persisting at equator or more distally, capsule distal surface often impressed in 4(–8) radiating lines.
turbinate, 4.5–6 × 4.5–6 mm.
short caudate distally, 1.5–2.5 mm.
Philadelphus microphyllus
Philadelphus microphyllus var. microphyllus
Varieties 5 (4 in the flora).
Within Philadelphus microphyllus as treated here, P. A. Rydberg (1905) recognized nine species, C. L. Hitchcock (1943) one species with eight subspecies, and Hu S. Y. (1954–1956) 11 species and four varieties, based on vestiture, leaf size and shape, and floral differences. Four varieties are recognized here within the flora area, with a fifth restricted to Mexico and without the needed varietal combination.
Two characters are particularly important in distinguishing the varieties of Philadelphus microphyllus: adaxial leaf blade cuticle thickness and vestiture. Adaxial leaf blade cuticles can be thin and papillate, closely reflecting the adaxial epidermis cells (as seen at 30–40\x) or can be thick and smooth. Leaves with thin cuticles dry brown due to brownish granules developing in the epidermis; those with thick cuticles dry gray-green, olive green, or yellowish green without granules in the epidermis cells. Sometimes both types occur in a leaf in either a tight or bold mosaic pattern or the leaf blade may be papillate and brown only along its margins.
Vestiture is mostly sericeous-strigose on leaves, stems, hypanthia, and sepals. The appressed hairs can be slender, short or long (0.2–1.5 mm), appressed, loosely appressed, ascending, or erect. The larger hairs have slender bases that allow them to be strictly appressed, but in some taxa, the base (upon drying) lifts and twists the hair upward, leaving the hairs oriented in many different directions; we refer to this condition as chaotic vestiture. In more densely vestitured plants, very slender, elongate, wavy-curved hairs form an understory beneath the more or less dense sericeous-strigose vestiture.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Four species that were recognized by P. A. Rydberg (1905) and Hu S. Y. (1954–1956) on the basis of hypanthium and sepal vestiture are here combined: Philadelphus argenteus and P. crinitus (densely lanate-sericeous-strigose, with underlying hairs more slender and coiled), P. microphyllus (glabrous or sparsely sericeous in four vertical lines), and P. occidentalis (uniformly sericeous-strigose, vestiture not completely obscuring the epidermis). The vestiture patterns are often mixed in populations, although regional patterns exist. Most plants in the northern range (northern Arizona, Colorado, southern Nevada, northern New Mexico, Utah, Wyoming) have sparsely sericeous-strigose adaxial leaf surfaces and a slightly denser vestiture on the abaxial surfaces; the adaxial leaf surfaces have a thin cuticle, and the leaves dry a brown color. In more arid zones (southeast Arizona, southwestern New Mexico, trans-Pecos Texas, and Baja California, Mexico), the adaxial epidermis often has a thicker, smoother cuticle or a mosaic of areas of thin and thick cuticle, and the leaves dry a gray- or olive green color.
The taxon crinitus, first named as a subspecies of Philadelphus microphyllus, is based on a population from the rhyolitic Davis Mountains in trans-Pecos Texas. Plants assigned to this taxon have densely vestitured hypanthia and sepals; longer hairs on the abaxial leaf surface (to 1.2 mm), with an underlying layer of thinner, wavy hairs; and thick adaxial cuticles. They are usually distinct from adjacent var. microphyllus. However, similar plants occur in the nearby limestone Guadalupe Mountains and again in southeastern Arizona (Huachuca and Santa Rita mountains) and in the intervening areas. Many from the latter region have been considered P. argenteus (with densely vestitured hypanthium and sepals, often similar leaf vestiture, and thick cuticles), but plants referable to P. argenteus occur scattered among plants of var. microphyllus and do not form large uniform populations; the P. argenteus form is here considered a more strongly vestitured phase within an expanded var. microphyllus, which then also includes var. crinitus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Hypanthia and sepal abaxial surfaces glabrous or sparsely to moderately sericeous, hairs not obscuring epidermis. | → 2 |
2. Leaf blade adaxial surfaces sparsely sericeous-strigose with appressed or slightly ascending slender hairs; leaf blade margins entire; inflorescences 1(–3)-flowered; capsules 4.4–6 mm; w United States, including se Arizona and sw New Mexico. | var. microphyllus |
2. Leaf blade adaxial surfaces sparsely to moderately strigose-sericeous with appressed or loosely appressed thick hairs mixed with erect hairs, or all hairs erect; leaf blade margins usually entire, on larger leaf blades sometimes sparsely serrulate; inflorescences 1–3(–5)-flowered; capsules 5–8 mm; mountains of se Arizona, sw New Mexico. | var. madrensis |
1. Hypanthia and sepal abaxial surfaces moderately to densely sericeous-strigose or villous-lanate, often with understory of thinner ± curled hairs usually completely obscuring epidermis except sometimes in fruit. | → 3 |
3. Leaf blade abaxial surfaces with hairs usually erect and chaotically oriented, sometimes appressed; mountains of sc New Mexico. | var. argyrocalyx |
3. Leaf blade abaxial surfaces with hairs appressed or loosely appressed; w United States, but mostly not sc New Mexico. | → 4 |
4. Leaf blade adaxial cuticles forming mosaic of thin, papillate areas and thick, smooth areas, adaxial surfaces drying mosaic of brown and yellowish gray-green, or cuticles uniformly thin, papillate, adaxial surfaces drying dark brown. | var. microphyllus |
4. Leaf blade adaxial cuticles thick, smooth, or papillate near margins, adaxial surfaces drying olive green or yellowish gray-green. | → 5 |
5. Leaf blade abaxial surfaces with appressed or loosely appressed hairs 0.5–1.2 mm; adaxial surfaces with only appressed or slightly ascending hairs 0.3–0.7 mm; w Texas to sw Arizona. | var. microphyllus |
5. Leaf blade abaxial surfaces with appressed or loosely appressed hairs 0.3–0.7 mm, adaxial surfaces with appressed hairs 0.1–0.6 mm and often with shorter erect hairs, 0.1–0.3 mm; California, adjacent w Nevada. | var. pumilus |
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