Malope trifida is an annual growing to about 3', sometimes bushy, sometimes with almost unbranched stems, and lobed leaves. The flowers are the usual mallow shape, but there are some features which make it easier to identify this species.
Moss Rose Portulaca spp.
Nasturtium Tropaeolum majus
Pot Marigold Calendula
Snow-on-the-Mountain Euphorbia marginata
Spider Flower Cleome spp.
Sweet Pea Lathyrus odoratus ...
These flowers also need to be seeded by about the 15th: asperula, asters, bells of Ireland, calendula, cosmos, dahlia tubers, daisies (English and African), dianthus, feverfew, gladiola corms, godetia, hollyhock, impatiens, kochia, layia, malope, malva, nemesia, nicotina, petunia, phlox, ...
See also: Growing, Spring, Seeds, Flower, Seed starting