California burclover

Probably most kids in Southern California are familiar with this weed, from having the burrs stuck in their socks after playing outside at recess or lunch (I remember being fascinated by the burr's spiral construction!).  There is rather a lot of it in our front yard this year for some reason, so I decided to look it up.  It is Medicago polymorpha, also known as burr medic, toothed bur clover, and, for some reason, California burclover -- it is not native to California at all, but to the Mediterranean, presumably the reason why it grows so well here.  In lawns it is usually short, most likely because it keeps getting mowed off, but when given its head it is long and sprawling, either along the ground or borne up by nearby plants. 

(Quite a number of online sources remark on its being called "California burclover" while native to the Mediterranean, but none of them wants to even hazard a guess as to why it is associated with California!)

Tall fescue

I thought this was one of the numerous crabgrasses, but apparently it is tall fescue (Festuca arundinacea). The crabgrass seed heads, as far as I can tell, all have that distinctive splayed-tines formation, while these stay quite close to the stem.  Yes, that's my shovel at the bottom of the photo! it's a weed in our yard.

The seedlings of crabgrass and fescue look remarkably alike.

Stinging nettle

A seedling (about 3 in./8 cm) of stinging nettle.

Stinging nettle, or Urtica dioica, bears on its leaves and stems a haze of tiny hair-like trichomes which act like hypodermic needles to inject histamines into the skin of humans and animals that touch it, producing a stinging sensation.  It has for centuries been used as a medicinal plant and a food source.

Stinging nettle can grow up to 3 to 7 ft. tall (1 to 2 m) in summer, and dies back in winter.  It grows in shady, damp areas -- it seems to come up more quickly here after a period of rain -- and spreads through rhizomes

The sting doesn't seem to be as intense when the plant is still small, so pull it up early if you can; otherwise, be sure to wear gloves!