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Walker's evening-primrose, Walker's sun-cup

Habit Herbs annual, glandular puberulent and sparsely villous. Herbs annual or short-lived perennial, villous, usually densely so proximally, less dense to glabrate distally, sometimes hairs somewhat appressed and shorter on leaves, also sometimes glandular puberulent on distal parts.
Stems

slender, unbranched or branched, 10–20 cm.

slender, unbranched or branched from base, 10–60 cm.

Leaves

primarily cauline;

petiole 0.3–1.8 cm;

blade unlobed, narrowly ovate to elliptic, 0.3–2 × 0.3–1 cm, margins entire or inconspicuously denticulate, brownish oil cells lining veins abaxially.

in basal rosette and/or cauline, often purple-dotted, 2–22 × 0.4–3.5 cm;

petiole 0.4–8 cm;

blade pinnately lobed, sometimes lateral lobes greatly reduced or absent and blade reduced to terminal lobe only, terminal lobe oblong or cordate to ovate, 1–5 × 0.5–3.2 cm, margins serrate, brown oil cells prominently lining veins abaxially.

Racemes

erect, elongating in fruit.

erect, elongating after anthesis.

Flowers

opening at sunrise;

buds without free tips;

floral tube 0.4–0.5 mm, glabrous inside;

sepals 1–1.2 mm;

petals yellow, fading pale lavender, 1–1.5 mm;

stamens 4 (or 8), antisepalous, filaments 0.5 mm, anthers 0.5–0.7 mm, glabrous, when 8, then antipetalous ones smaller and abortive;

style 1.5 mm, stigma surrounded by anthers at anthesis.

opening at sunrise;

buds individually reflexed, with apical free tips less than 1 mm;

floral tube 0.5–1.5 mm, glabrous or sparsely villous inside;

sepals 1.5–5 mm;

petals bright yellow, fading pale orange or lavender, 1–6 mm;

stamens unequal, filaments of antisepalous stamens 1–3 mm, those of antipetalous ones 0.3–2 mm, anthers 0.5–2 mm, glabrous or sparsely ciliate;

style 1.5–6 mm, stigma surrounded by anthers at anthesis.

Capsules

spreading or reflexed, clavate, 4–10 mm;

pedicel 3–9 mm.

spreading or ascending, oblong-cylindrical, 11–45 mm;

pedicel 5–30 mm.

Seeds

0.8 mm.

0.6–1.2 mm.

2n

= 14.

Chylismia exilis

Chylismia walkeri

Phenology Flowering Apr–Jun.
Habitat Calcareous sand, gypseous clay flats, juniper woodlands.
Elevation 1000–1900 m. (3300–6200 ft.)
Distribution
from FNA
AZ; UT
[BONAP county map]
sw United States
[WildflowerSearch map]
[BONAP county map]
Discussion

Chylismia exilis, known from Kane and San Juan counties in Utah and northern Coconino and Mohave counties in Arizona, is cryptic due to its small size. It may not be as rare as assumed, since it is difficult to spot in the field. P. H. Raven (1962, 1969) determined this species to be self-compatible and autogamous.

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

Subspecies 2 (2 in the flora).

P. H. Raven (1962, 1969) determined this species to be self-incompatible and primarily autogamous.

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

Key
1. Leaves primarily cauline, rarely forming inconspicuous basal rosette, lateral lobes usually greatly reduced or absent; petals 1–3 mm; anthers 0.5–0.8 mm.
subsp. walkeri
1. Leaves primarily basal, forming conspicuous rosette, cauline reduced or absent, lateral lobes usually well developed; petals 2.8–6 mm; anthers 1–2 mm.
subsp. tortilis
Source FNA vol. 10. FNA vol. 10.
Parent taxa Onagraceae > subfam. Onagroideae > tribe Onagreae > Chylismia > sect. Chylismia Onagraceae > subfam. Onagroideae > tribe Onagreae > Chylismia > sect. Chylismia
Sibling taxa
C. arenaria, C. atwoodii, C. brevipes, C. cardiophylla, C. claviformis, C. confertiflora, C. eastwoodiae, C. heterochroma, C. megalantha, C. multijuga, C. munzii, C. parryi, C. scapoidea, C. specicola, C. walkeri
C. arenaria, C. atwoodii, C. brevipes, C. cardiophylla, C. claviformis, C. confertiflora, C. eastwoodiae, C. exilis, C. heterochroma, C. megalantha, C. multijuga, C. munzii, C. parryi, C. scapoidea, C. specicola
Subordinate taxa
C. walkeri subsp. tortilis, C. walkeri subsp. walkeri
Synonyms Oenothera exilis, Camissonia exilis Camissonia walkeri, Oenothera walkeri
Name authority (P. H. Raven) W. L. Wagner & Hoch: Syst. Bot. Monogr. 83: 207. (2007) A. Nelson: Bot. Gaz. 56: 66. (1913) — (as Chylisma)
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