Flora of North America species comparison

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Rhinotropis

Rhinotropis acanthoclada

milkwort

desert milkwort, desert polygala, thorny milkwort
Habit Herbs, perennial, subshrubs, or shrubs, single- or multi-stemmed, with or without thorns, then as modified tips of racemes. Shrubs or subshrubs, single- to multi-stemmed, (1.5–)2–10(–12) dm.
Stems

usually sprawling to erect, sometimes prostrate or decumbent, usually not glaucous, pubescent or glabrous.

sprawling to erect, densely pubescent to glabrate, hairs spreading and short.
Leaves

alternate;

sessile, subsessile, or petiolate; usually not strongly dimorphic;

blade surfaces pubescent or glabrous.

sessile or subsessile;

blade oblanceolate, narrowly obovate, or narrowly elliptic, 3–25 × 1–5 mm, base long-cuneate, apex rounded or acute, surfaces usually densely pubescent, rarely subglabrous, hairs spreading and short.
Racemes

terminal, sometimes appearing axillary if poorly developed, sometimes aggregated into pseudopanicles or reduced and appearing fasciculate, 0.5–2.5 ×0.6–2 cm;

rachis thorn-tipped;

peduncle 0–0.2(–0.5) cm, often poorly developed;

bracts deciduous, lanceolate.
Inflorescences

terminal or leaf-opposed, sometimes appearing axillary if poorly developed, racemes, sometimes reduced and appearing fasciculate or aggregated into pseudopanicles;

peduncle present or absent;

bracts deciduous to subpersistent or persistent.

Pedicels

present.

1.5–4(–5.8) mm, usually shorter than flowers, pubescent, sometimes sparsely so.
Flowers

cream, yellowish green,yellow, white, pink, rose, or purple, cleistogamous usually absent, sometimes present (in R. californica and R. lindheimeri), (2.4–)3.5–14.5 mm;

sepals deciduous or persistent (when persistent, usually only upper; all persistent in R. rusbyi), sometimes appearing very slightly connate basally, pubescent or glabrous;

wings deciduous, 2.5–12.5 mm, glabrous or pubescent;

keel usually beaked with unlobed projection, beak sometimes reduced or obscure (rarely on all flowers unless cleistogamous, and then inflorescence usually proximal), keel glabrous or pubescent;

stamens usually 7 or 8, rarely 9 (in R. acanthoclada), in chasmogamous flowers, fewer in cleistogamous flowers, not grouped;

ovary 2-loculed.

cream to yellowish green, wings cream to greenish, upper petals often purple-tipped, distal keel often dark yellow to green, (3–)3.5–5(–5.3) mm;

sepals deciduous, ovate to elliptic, 1.6–3.5 mm, spreading-pubescent, margins usually ciliate;

wings obovate, 3–5 × 2–3 mm, glabrous or sparsely pubescent;

keel 2.7–3.8 mm, sac glabrous, beak absent or obscure and bluntly rounded, to 0.7 × 0.5 mm, glabrous;

stamens rarely 9.
Fruits

capsules, dehiscent, margins winged or not, glabrous or pubescent.

Capsules

ellipsoid or slightly obovoid, (3–)4–6 × 2.5–4 mm, base rounded or, sometimes, cuneate, margins with very narrow and even wing, glabrous.
Seeds

pubescent to subglabrous, arillate.

3.2–4.2 mm, pubescent;

aril 1–1.7 mm, lobes to 1/3 length of seed.
x

= 9.

2n

= 18.

Rhinotropis

Rhinotropis acanthoclada
Phenology Flowering (early spring–)spring–summer(–late fall).
Habitat Usually on loose silts or sands derived from limestone, granite, sandstone, or gypsum in open places or slopes in desert scrub or juniper woodlands.
Elevation 800–1800 m. [2600–5900 ft.]
Distribution
w United States; sc United States; Mexico; Central America (Guatemala)
[BONAP county map]
from FNA
AZ; CA; NV; UT
[WildflowerSearch map]
[BONAP county map]
Discussion

Species 17 (12 in the flora).

Of the 17 species of Rhinotropis ranging from the southwestern United States and/or Mexico, only R. purpusii (Brandegee) J. R. Abbott extends into Guatemala. Of all the genera treated here, this is the only one that has been monographed within the last 100 years (T. L. Wendt 1978). Rhinotropis is probably sister to the Caribbean clade Phlebotaenia Grisebach, and appears to be fairly closely related also to the pantropical (although predominantly neotropical) genus Securidaca Linnaeus. Rhinotropis is largely endemic to arid regions but some species (R. californica) occur in mesic areas.

The flower beak is a cylindric, conic, or contorted non-fimbriate hollow projection from the lower (or central) apex of the keel region. It is highly reduced or absent in some species. The other diagnostic features of Rhinotropis are also not monothetic across all species. Many species have the upper sepal persistent in fruit and the other sepals, including the wings (and the corolla), deciduous. Unlike other North American Polygalaceae, species of Rhinotropis often have five petals; the lateral petals are much reduced, linear, and adnate for most of their length to the staminal column; additionally, several species are shrubs and a few have thorn-tipped inflorescence axes.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

In northern Arizona and southern Utah, Rhinotropis acanthoclada overlaps geographically with R. intermontana and tetraploid hybrids are known (T. L. Wendt 1978, 1979).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Shrubs or subshrubs; racemes thorn-tipped; sepals deciduous.
→ 2
2. Flowers (2.5–)3–5(–5.3) mm; sepal wings usually cream or greenish; keel petals without beaks or beaks to 0.5–0.7 mm; stems densely pubescent to glabrate, not glaucous.
→ 3
3. Leaves and stems densely pubescent, with short, spreading hairs; pedicels 1.5–4(–5.8) mm, usually shorter than flowers, pubescent; non-wing sepals pubescent, hairs spreading.
R. acanthoclada
3. Leaves densely pubescent with incurved hairs, stems densely pubescent or glabrate, hairs matted or shaggy, appressed, incurved or, sometimes, spreading; pedicels (2.5–)3–7(–9) mm, usually longer than flowers, glabrous; non-wing sepals glabrous or subapically sparsely hairy.
R. intermontana
2. Flowers (6–)7–14.5 mm; sepal wings usually pink, sometimes light green; keel petals with prominent beaks (1–4 mm); stems glabrous or pubescent, often glaucous, at least when young.
→ 4
4. Keel petal beaks with 1 or 2 prominent invaginations along abaxial side (formed by sinuate excess tissue); seeds most densely pubescent apically, proximal 1/2 sparsely and unevenly pubescent or glabrous.
R. heterorhyncha
4. Keel petal beaks entire or slightly erose; seeds ± evenly and moderately densely pubescent, occasionally with glabrate patches.
R. subspinosa
1. Herbs, subshrubs, or shrubs; racemes usually not thorn-tipped (except usually weakly thorn-tipped in R. rusbyi, then all sepals persistent in fruit); upper sepal persistent in fruit or all deciduous.
→ 5
5. Flowers (2.5–)7–14.5 mm (smaller cleistogamous flowers sometimes present in R. californica proximally); sepals all deciduous or all persistent.
→ 6
6. Sepals persistent; racemes usually weakly thorn-tipped (often not clearly visible when young); Arizona.
R. rusbyi
6. Sepals deciduous; racemes not thorn-tipped; California, Oregon.
→ 7
7. Keel petal beaks oblong, usually notched or contorted, rarely subentire, 0.7–1 mm wide distally; cleistogamous flowers often present, 2.4–5 mm, chasmogamous flowers 9–14.5 mm; perennials, 0.5–3.5 dm; stems laxly erect, decumbent, or prostrate.
R. californica
7. Keel petal beaks linear, entire, 0.2 mm wide distally; flowers all chasmogamous, 7–14 mm; perennials, subshrubs, or shrubs, 1–25 dm; stems erect to sprawling or decumbent.
R. cornuta
5. Flowers (2.4–)2.9–7.5(–7.7) mm; upper sepal persistent, others deciduous.
→ 8
8. Racemes usually leaf-opposed; keel petals usually with glabrous sacs, beaks (0–)0.5–2 mm; leaf blades usually elliptic, ovate, obovate, lanceolate, or linear, sometimes scalelike, (3–)4–35(–40) mm.
→ 9
9. Roots with brown, gray, or dull red-brown cortex, not exfoliating.
R. lindheimeri
9. Roots with prominent bright orange-red cortex, loosely exfoliating.
R. nitida
8. Racemes terminal, sometimes appearing axillary, but not leaf-opposed; keel petals with incurved-puberulent sacs in distal 1/2, beaks small, occasionally to 1.1 mm; leaf blades usually scalelike, linear, linear-subulate, lanceolate, elliptic, obovate, or ovate, 1–5.9(–15) mm.
→ 10
10. Herbs often loosely mat-forming; stems prostrate to laxly erect, not glaucous, glabrous or very sparsely pubescent; leaf blades elliptic, obovate, ovate, or scalelike, (1.5–)2–5.9(–8) mm.
R. rimulicola
10. Subshrubs broomlike, not mat-forming; stems usually erect, glaucous and glabrous, or not glaucous and sparsely puberulent, rarely glabrate; leaf blades often scalelike, sometimes elliptic, linear-subulate, lanceolate, or obovate, some early deciduous, appearing absent, 1–4(–15) mm.
→ 11
11. Flowers pink; capsule bases cuneate; seed bodies often more sparsely pubescent to subglabrous in distal 1/5–1/2; stems usually glaucous, at least proximally, and glabrous.
R. maravillasensis
11. Flowers usually white or cream, often with purplish center stripe, rarely pink; capsule bases rounded or subtruncate; seed bodies usually evenly pubescent; stems not glaucous, usually sparsely pubescent, rarely glabrate.
R. nudata
Source FNA vol. 10. FNA vol. 10.
Parent taxa Polygalaceae Polygalaceae > Rhinotropis
Sibling taxa
R. californica, R. cornuta, R. heterorhyncha, R. intermontana, R. lindheimeri, R. maravillasensis, R. nitida, R. nudata, R. rimulicola, R. rusbyi, R. subspinosa
Subordinate taxa
R. acanthoclada, R. californica, R. cornuta, R. heterorhyncha, R. intermontana, R. lindheimeri, R. maravillasensis, R. nitida, R. nudata, R. rimulicola, R. rusbyi, R. subspinosa
Synonyms Polygala section rhinotropis Polygalaacanthoclada a.
Name authority (S. F. Blake) J. R. Abbott: J. Bot. Res. Inst. Texas 5: 134. (2011) (A. Gray) J. R. Abbott: J. Bot. Res. Inst. Texas 5: 134. (2011)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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