Coryphanta cornifera

Coryphanta is somewhat under-appreciated genus of mostly Mexican plants. It has been in cultivation for over 100 years, and Coryphanta cornifera is one of the old classics.
The genus Coryphanta has plants that will find place in any common 'eclectic' collection, and also is a good choice of specialization. Plants vary in shapes and spinaton, and lots of forms of otherwise well-known plants are discovered recently. 

Mammillaria melanocentra

Mammillaria melanocentra is a 'classical' Mammillaria, a distinct plant that has been around. It is a larger plant with slightly blueish step and large for the genus flowers, that on mature plants come in proper rings. Each areole has a prominent black central spine, hence the name.

Trichocereus hybrid 'red'

This unnamed Trichocereus hybrid I bought some tome ago from the garden store, with grafting in mind. Something got on the way and that grafting project got postponed for a while, and in the meantime the plant bloomed. After seen the flowers it was spared from becoming a grafting stock, and 'lives happily ever since'. It usually produces one or two flashes of that beautiful red flowers per season, and I use it to make seeds crossing with other Echinopsis hybrids I have.

Echinocactus grusonii

Echinocactus grusonii is a common 'golden barrel' cactus, easily available in stores. It blooms at a size of basketball or larger, and requires lots of sun. Here in Central California it can be planted outside, and grows well. It tolerates light frost, but when exposed to it the plants start developing unnatural side shoots.
Flower looks unusual for both Echinocactus and Ferocactus, with needle-like pointy petals. The blooms come from the felt that this plant develops at it's top once mature.
There is a lot of story around this species. Despite been probably the most commonly sold cactus, it's main habitat area is destroyed - sunk under the artificial lake. There are some newly discovered locations of this plant though. It is commonly accepted now that this species is actually of natural hybrid origin, with parents coming from Ferocactus and Echinocactus genera. The plant is commonly viewed as a golden ball, but really old plants in habitat are actually growing taller than 6 ft, with stem wrinkled like an elephant leg.

Mammillaria petterssonii

Mammillaria petterssonii - another beautiful Mammillaria. This attractive form with yellow spines is common in garden stores. It is a large growing plant, slowly forming a clump of boll-shaped heads. Larger plants, like the one in the picture, will show hundreds of open blooms per time.
Here in Central CA Mammillaria petterssonii can be grown without cover year-round, but will develop somewhat slower.

Mammillaria teresae

Mammillaria teresae is a small plant with large underground taproot. This plant is popular but not too easy to get - mainly due to the fact that each fruit contains just a few seeds and it stays embedded into plant body when ripe. Extracting seeds is a meticulous and slow procedure.
The plant is generally easy in culture but not for the beginners - mainly because it can not grow in "Cactus soil" available from the stores and needs a stable culture, something that takes time for everyone to establish.

Nyctocereus serpentus

Nyctocereus (Peniocereus) serpentus is probably the oldest cactus been in cultivation for nothing but it's flowers. It is known to be grown in before-Columbus time, and has no recognized use value. The plant without blooms is easy to call ugly - the stem is nothing but a spiny stick, usually somewhat deformed and scarred. The large fragrant flowers get cactus aficionado stunned.
It is interesting to watch the flowers of Peniocereus serpentus open. The process starts once it is completely dark, at around 10-11pm here in Bay Area, and it takes about half an hour for the flower to go from slightly inflated blob to the full open marvel.
In the morning flowers wither quickly on a sunny day, or may me still open at 9or 10am if the morning is cloudy.