The question wants us to spot the weed that behaves as an ephemeral, meaning it completes several short life cycles in one growing season rather than one long cycle.
- Stellaria media: This weed finishes germination to seed shedding in about five to six weeks and can throw up multiple generations in a single season, which is the hallmark of an ephemeral weed.
- Phalaris minor: This grassy weed of wheat fields follows one normal season long life cycle, so it is a simple annual, not an ephemeral.
- Medicago denticulata: This is a winter season annual with a single full cycle each year, again not ephemeral in habit.
- Phyllanthus niruri: This broadleaf weed also completes just one season length cycle rather than repeating quickly.
Only Stellaria media shows the rapid, repeated life cycle that defines an ephemeral weed, so option 1 is correct.
Let's summarize:
- Ephemeral weeds complete germination to seed set in a few weeks and repeat several times a season.
- Stellaria media is the textbook example of this habit among the given choices.
So the final answer is Stellaria media.