Lithops species
Lithops are the classic "living rocks." They are small, beautiful gems, popular since the 1960's, and deservedly so. A few are tricky in cultivation, but many are reasonably easy, as long as you're careful with their lighting and watering requirements. I'm very much a beginner with these species, but here are some that I've found easy to keep:
Lithops aucampiae ssp. eniceae v. fluminalis C54
Lithops karasmontana v. tischeris C182
Lithops lesliei v. hornii C15
Lithops lesliei subsp. lesliei v. venteri C1
Lithops schwantesii C79
Growth Habit: Tiny, a few cm high at most, with extremely succulent, paired leaves, between which their flowers appear. Mostly interesting for the patterning on the tops of the leaves.
Scientific name: Lithops N.E. Brown
Taxonomy: The genus was described by N.E. Brown in 1923. Desmond Cole is undoubtedly the best known of Lithops taxonomists, so you'll often see lithops' species names followed by a "C" number, as in my list above.
Distribution: From Namibia east through the Northern Cape and mostly east to Limpopo in South Africa.
Cultivation: As much sun as you can give, year around. Watering is more problematic, but this is what has worked for me, for these species: Summer, no water. Around late August or early September, they start to perk up, and most start to show flower buds. From then until their flowers start to fade, I water them weekly. After that, they're kept bone dry until their old leaves dry up. In late spring the ones whose leaves have completely dried up get a little spritz.
Emerging flower buds:
Flowers: Not terribly interesting, typical flowers from the Aizoaceae/Mesembryanthemaceae. Most are yellow, some white. Sometimes the yellow flowers fade to red, as in this L. aucampiae ssp. eniceae v. fluminalis, and I think they look better that way:
Minimum temperature: Lithops grow in a variety of environments, and some of them undergo temperatures below freezing. The few that I have flower well with a minumum of 50 degrees.
Conservation Status: A few lithops are considered vulnerable or near threatened, but none of the above are protected.
Observations: You can often find grossly overgrown, bloated (some over 4" tall) lithops in big box stores and garden centers. I don't have any personal experience with these, but from what I've read, it's very difficult to keep them alive and bring them back to their normal state.