Calylophus hartwegii (Benth.) Raven
 

By Nicolas Umstattd, Native Plants of Arizona 2007
Common names: Hartweg’s sundrops, evening primrose, western primrose (1)
Family: Onagraceae
Synonomy: Galpinsia hartwegii (Benth.) Britt. Oenothera hartwegii Benth. Oenothera hartwegii var. typica Munz. Salpingia hartwegii (Benth.) Raimann (2)
Etymology:  This species was named after Karl Theodore Hartweg, a German Botanist. (1812-1871) Hartweg was empoloyed by the London Horticultural Society to explore the vast number of unkown species in the Americas. He spent much of his time in Mexico, Central America, and Southern North America, namely California. He is responsible for cataloging numerous species of orchids and some coniferous trees, in Northern Mexico. Hartweg spent seven years in the Americas on his first trip and later returned to continue in his work. . 

Identification
Growth form: Clump forming herbaceous perennial (4)
Roots: Taproot
Stem:  Many branched stems, 10-40 cm long, woody at base.(4)
Leaves:  Alternate lanceolate to linear 5 cm long and 1-8 mm wide, simple and entire, shiny green. (4)
Inflorescence/Flowers: solitary in upper leaf axils, inferior ovary, hypanthium tube 2-6 cm long dilated upwards, 5-12 mm wide at summit, sepals 10-15mm, linear petals 8-25mm, bright yellow color aging to pink. (5)
Fruit: Elongated capsule 1.5-2 cm long, narrowed at base. (4)
Similar species:  Oenothera, has  4 cleft stigmas, and pollen hanging in long strands. Calylophus has a peltate stigma.(6)

Ecology
Life history: Herbaceous perennial (4)
Native/ introduced: native (4)
Photosynthetic pathway: C3
Phenology: April to September. Flowers open late afternoon or evening, wilting the following day, pollinated by moths. (6)
Distribution:  4,000- 7,000 feet. Dry mesas, limestone hills, plains, and savannahs.  In Arizona: Apache, Navajo, and Coconino Counties. Arizona to Texas and north to Kansas, Colorado and Oklahoma. Also found in Mexico (4). 

Uses: Cultivated ornamental

References:

(1)     1. USDA, NRCS 2007. The PLANTS database, (http://plants.usda.gov/). National Plant Data Center, Baton Rouge, LA

(2)     2. Integrated Taxonomic Information System (IT IS) on-line database. (http://www.itis.gov/index.html)

(3)     3. Orchids.co.in. Orchid Plant Care www.orchids.co.in/orchidologists/karl-theodore-hartweg.shtm

(4)     4. Ecological Restoration Institute. Plants of Nrothern Arizona Forests. A Comprehensive Field Guide for  the  Mogollon Plateau Coniferous Forest Bioregion in Arizona. Field Testing version 2007

(5)     5. Macdougall, Walter B. 1973. Seed Plants of Northern Arizona. Society of Science and Art Incorporated. Flagstaff, Arizona

(6)     6. Cronquist, Arthur and Noel H. Holmgren and Patricia K. Holmgren. 1997. Vascular Plants of the Intermountain west. Volume 3 part A. New York botanical Garden. Bronx, New York

(7)     7. Lady Bird Johnson Wildflower Center (http://www.wildflower.org/)

(8)     8. Epple, Anne O. and lewis E. Epple. 1995. A Field Guide to the Plants of Arizona. Falcon Press Publishing Company. Helena, Montana