Unfortunately we cannot identify this plant for you at this stage of its development, but we believe it is a weed. If you didn't plant this, chances are its a weed from a wind blown seed or bird dropping. If it is growing in your garden bed we suggest you pull it out so it doesn't compete for light, nutrients and water with your other cultivated plants. If you have the room and want to watch it grow leave it be; just remember once it is done blooming it will begin to drop seed and disperse throughout your garden. Suggest you show your photo and a sample of the plant to a horticulturist at you local garden center or weed specialist at the university cooperative extension service to see if they can help identify for you. If you find out, please let us know as this is how we learn as well.
This looks like purslane, a succulent annual that grows quickly from seeds. It especially flourishes in bare areas in the lawn. Since it is an annual your efforts at control should be the following: Dig all you see now to prevent them from going to seed in your lawn. Rake bare areas in the lawn, top-dress with a little loam or mix of loam and compost, and over-seed thickly with grass seed in April of next year. The thicker and healthier your grass, the fewer weeds you will have of all types. Have the pH of your lawn tested and lime only if needed. Next spring if you want to prevent this weed from germinating again you can use a pre-emergent herbicide according to directions. Ask at your local garden center for product recommendations.
We can't say for sure, but it looks like poison ivy. We would need a clearer photo to be positive. Until you find out for sure, please don't touch the plant. The adage "leaves of 3, let it be" is important for poison ivy because it can be a clump, shrub or a woody vine. Found most everywhere, it adapts to sun or shade conditions, various soil types, as well as wet or dry environments and can have different leaf shapes. But usually when the plant is young, its stems are a light reddish-green and can be hairy or hairless. When the plant matures more, the stems become brown and woody. If it is growing in your garden as a volunteer, suggest you dig it out as a precaution and wear gloves in case it is poison ivy. Dispose in the trash, not a compost pile.
Based on the plant size and location and without being able to closely examine a leaf, this appears to be the Common Mallow weed. Here are some characteristics of Common Mallow that can help confirm its identity. Mallow leaves are 3/4 to 1 1/2-in. in diameter and are toothed around the edge. This fast growing weed also has a blossom that is white to pink, with 1/2- to 3/4-in. flowers. Common Mallow can grow 4 in. to 2 ft. tall. It appears to have already spread which is indicative of weed behavior. Reproduction is by seeds, but fragmented stems can root at the nodes if conditions remain sufficiently moist for a long enough period of time. If it is Common Mallow, you're correct in assuming it could take over this flower bed!
We think this is a species of Taxacum although there are similar weeds, most developing foliage with jagged edges, daisy-like flowers and fuzzy seed heads that become more garden weeds. If you don't want hundreds of seeds to develop, suggest you cut off at least the flowering head before the seeds disperse. Here's a rundown on the Asteraceae family: http://www.wildflowers-and-weeds.com/Plant_Families/Asteraceae.htm The reason why we do not believe this is common groundsel, S. vulgaris, is that it bears tiny clusters of flowers that show color without ever really opening until they go to seed as well as deeply lobed leaves. It also is part of the Asteraceae family and both are related. Like the dandelion, if you don't want it to spread, pull up before it sets seed.
Your plant appears to be Japanese knotweed, an aggressive weed that is difficult to eradicate. You'll need to dig up every last bit of root. Then, as bits of root you miss send up new leaves, dig those out too. You can win against this plant - in the long run! Mowing or cutting back greatly reduces the strength of this perennial plant (at any season). Preventing those blooms from going to seed will reduce next year's "crop" of weeds. And after cutting back (or over the winter), try covering the area with cardboard, or several layers of newspaper. Water well and mulch over top of this, and keep an eye out for rogue sprouts appearing in spring. If you choose to apply herbicide, this is one of the best times of year to do it.
This may be poison ivy. The adage "leaves of 3, let it be" is important for poison ivy because it can be a shrub or a woody vine. Found most everywhere, it adapts to sun or shade conditions, various soil types, as well as wet or dry environments and can have different leaf shapes. When the plant is young, its stems are a light reddish-green to red and can be hairy or hairless. When the plant matures more, the stems become brown and woody. In the summer, the leaves tend to have a shiny coat, making it difficult to spray with a product to kill it. Also forms tiny flowers in the summer followed by berries. If it is growing in your garden , we suggest you dig it out and wear gloves. Dispose in the trash, not a compost pile, and do not burn as the toxins will become airborne.
This appears to be Frost Aster, a gorgeous natural aster found in prairies and woodlands in the region. Frost aster is an easy plant to grow, so easy that it is often considered a little "weedy". It's a great plant to grow if you have a lot of room and don't mind a lot of volunteer seedlings popping up. Frost aster needs full sun to partial shade. Because of its "weedy" nature it is great at colonizing disturbed and "waste places". It protects soil from erosion and provides food for wildlife where more sensitive plants cannot yet grow. It is called frost aster because it continues blooming late into the fall, unfazed by frosty nights. Because of its late blooms it is extremely valuable to pollen and nectar eating insects which don't have as many food options in the late fall.
Your plant may be a milkweed; please send a long shot of the entire plant, showing its growth habit and size and we'll confirm. Milkweed is a native perennial plant that is about 2-3' tall. This species is sometimes grown in gardens designed to attract butterflies (especially monarchs). The nectar of the plant attracts many other species of butterflies and insects as well. This is a very drought tolerant plant that often reseeds through the garden. We can't see the top so it could be either. Milkweed will have a white milky substance if you snap off a branch or leaf. Both are liked and both are hated. If you didn't plant it it is taking the water and nutrients from your cultivated plants so you have a choice as to what you want to do with it.
In the fall-winter in southern California, clusters of bright green clover-like leaves followed by long stems topped with clusters of inch wide, bright yellow flowers from late winter-spring. It has become an invasive plant along the coast of California. Underground corms must be completely removed to eliminate this prolific plant, even if a small bit of the corm is left behind, it will return again. Plus once the flowers are spent, multitudes of seeds are dispersed. To prevent this, carefully hand remove the weed making sure you have the entire corm/bulblet and then sprinkle the area with a pre-emergent formulated for Oxalis to prevent any seeds from germinating, but do not apply the pre-emergent in an area where you are planting cultivated seeds.