Ephemeral

A plant that completes its life cycle in short time period; being less than a growing season. There may also be more than one life cycle achieved within a year. An ephemeral plant can also be considered a short-term annual. A number of weeds are ephemeral plants, including:
• Groundsel (Senecio vulgaris).
• Common Chickweed (Stellaria media).
• Hairy Bittercress (Cardamine hirsuta).
• Thale Cress (Arabidopsis thaliana).
• Annual Meadow Grass (Poa annua), which can often behave as an ephemeral.