PlantFiles: Hartweg's Sundrops
Calylophus hartwegii

I have this plant growing in both full sun and part sun here in Oklahoma. It does equally well in either situation. It will tolerate quite a lot of shade. Naturalizes well, but is not invasive. Its blooms look like a primrose but with slightly smaller flowers and they stay open in the afternoon.

Hartweg's Sundrops is native to Kansas, Oklahoma, Colorado, Arizona, New Mexico, and Texas and parts of Northern Mexico. It's not endemic to Texas as has been stated. I've seen it growing in the short grass prairies in and around Elkhart, KS growing on sandy soils in well drained short grass prairies. It also grows in the nearby Cimarron National Grassland. I've seen it growing in Barber County near Medicine Lodge, KS also in short grass prairie.

It grows in well drained open prairie mostly and appears to thrive in hot dry situations. I had a couple in my garden in loose well drained soil until they got shaded out by a near-by tree and they slowly died. While they were there, they never needed watering and they bloomed for long periods each summer. If we had an extended drought they did bloom more if I gave them a little extra water, but they didn't need it to remain healthy. The blooms don't last long, but the plants produce new blooms daily. It's a great very tough drought tolerant plant for that full sun hot dry spot in your garden where most other things fry or need lots of extra water.

For me, this plant is a short-lived perennial; they usually grow for about 3-4 years and then need replacement. But for those years, they can't be beat. They put on a huge show of lemon yellow flowers in the late spring/early summer, a few scattered blooms during the high heat, and another flush in the early to mid fall. They take direct to reflected sun well, and are doing well in a fairly heavy soil. They do need supplemental water in our middle-desert summers.

Hartweg's Sundrops Calylophus hartwegii is Endemic to Texas.