Euphorbia aeruginosa (Miniature saguaro)

This euphorbia is a South African native, not found in the wild in North America. Though often called miniature saguaro, these are completely unrelated to saguaros.

Plants: Plants are succulent subshrubs up to 1′ (30 cm) in height, with blue-gray or brownish-green stems that are roughly square in cross-section and about ⅜″ (1 cm) on a side. Spine groups appear along the edges of the stems; spines are dark orange-brown and about ⅜″ (1 cm) in length.

Flowers: Small bright yellow cyathia (petal-like modified leaves), appearing near the stem tips. A female flower and several male flowers occur in a group.

4/6/2011 · Howard Peters Rawlings Conservatory & Botanic Gardens, Druid Hill Park, Baltimore, Maryland · ≈ 12 × 14″ (29 × 34 cm)

Kingdom	Plantae	Plants, but not fungi, lichens, or algae (from Stearn's Botanical Latin)
Subkingdom	Tracheobionta	Vascular plants—plants with a “circulatory system” for delivering water and nutrients
Division	Magnoliophyta	Flowering plants, also known as angiosperms
Class	Magnoliopsida	Dicotyledons—plants with two initial seed leaves
Subclass	Rosidae	Roses, legumes, proteas, dogwoods, hydrangeas, mistletoes, euphorbias, grapes, many more
Order	Malpighiales	A broad group encompassing 16,000 species
Family	Euphorbiaceae	Euphorbia or spurge family
Genus	Euphorbia	An extremely diverse-looking genus of mostly tropical and subtropical succulent plants. For Euphorbus, corpulent Greek physician of Juba II, King of Mauretania. Literally, “euphorbia” means “well-fed”
Species	aeruginosa	From Latin aerūgō, “[blue green] rust of copper, verdigris,” and‎ -ōsus.

About plant names...