From SporeWiki, the knowledge base dedicated to Spore

Template:FloraCreationInfobox The Zregen is a plant on the Ptashki homeworld. It has the unique characteristic of combining branches to form a solid joint. On rare occasions, it can join with other plants. Though not recreatable in Spore, it will appear as a branched tree with branches coming together at the end. It will also appear in the hut, because of how it is used.

[edit] Ptashki Uses

The discovery of manipulation of this plant sparked the tribal age for Ptashki. They mold its branches into a cage of various shapes and sizes. A large Zregen is used as the base for the hut, allowing it to float a few feet above the air. This helps protect babies. In the city, buildings are still made of Zregen, but due to cross-breeding and genetics, very large plants a few stories high connected with even more Zregen form large, multi-storied flats.