Plant ID please tiny white flowers 4 petals, not shepherd's purse

[Kalim8]

Hello, there's a lot of this plant growing on a bareish patch of lawn that's been under the trampoline for ages, so it's rather shady.

The leaves seem to be smooth with little hairs along the edges, up the stems, the leaves appear one at a time, and on opposite sides, but there's a clump of leaves at the bottom.

Possibly Thale Cress, Arabidopsis thaliana. Are the basal leaves simple in outline or do they have leaflets?

Thanks for replying, I don't think it is thale cress as the stalk doesn't have those long spiky looking things. The basal leaves look like this - they are hairy and have little bumps - I feel like someone unfamiliar with chess referring to a knight as a "little horsey"

Possibly a Brookweed
here

Thank you - I don't think it's that either as the brookweed leaves are a different shape.

Thanks for replying, I don't think it is thale cress as the stalk doesn't have those long spiky looking things. Not sure what you mean by this. Long spiky things on yours? On thale cress? leaves look OK for thale cress.

Could we have a close up of the flowers, please? That would at least get us to family.

I see you have dandelion leaves in the background ... did you know there's nearly 250 species of them?

You could subscribe temporarily to the facebook group Wildflowers of Britain and Ireland - there's good people on there, including some of the authors of the classic field guides. Don't make it too obvious that it's in a garden.

Note the brookweed has 5 petals. Hard to see from the photo, but I'm guessing your plant has 4?

Hard to see from the photo, but I'm guessing your plant has 4? Stupid of me - you say it has 4 in your title. The combination of 4 petals and the overall look of it suggests it's in the cabbage family, Brassicaceae, which is why you considered and dismissed Shepherd's Purse. There are some other families which have 4 petals, but none spring to mind as being right for this. A close up of the flower would help. If you find it difficult to focus on the flower, because the camera keeps focusing on the ground or a distant leaf, hold a piece of paper or even your hand just behind it - then the camera will focus on that, and the flower is close enough to be in focus.

I'm hoping it's Thale Cress - it's a very special plant - it was the first plant to have its genome sequenced.

Hello, what I was calling spikey things may have been what was left after the flowers had gone - this is the best close up I could get, I'm not impressed with my phone's camera

I also found this nearby, with very obvious "spikey bits" - that's very interesting about thale cress, wonder why it was chosen for sequencing.

I don't see anything to suggest that it isn't Thale Cress. And mine has the same "spiky bits" - as you say, remains of flower stems.

It's small, has abundant seed, and a short life cycle - 6 weeks, which makes it ideal for genetic research. It's been used since about 1900, it's been described as the plant equivalent to fruit fly (Drosophila) - anyone doing an OU genetics course will have fond memories of breeding fruit flies in the living room and watching the inheritance of red or brown eyes. So since it was so much used in researcj already, it was an obvious first choice.

Your second specimen is one of the bittercresses, Cardamine sp. It'll be one of these 5

Great! Thank you very much for sharing your expertise, MereDint.