Cleistocactus strausii
Silver Torch cactus can thrive in low-nitrogen soil without facing the consequences of low nitrogen. Too much water will make the plant weak and lead to root rot. 
Least Concern. This cactus is locally abundant in its native land and has few local threats to its survival.
This cactus can be propagated by cuttings or seed.
Sudbury River
Water caltrop, more commonly known as water chestnut, species "Trapas natans", is an invasive waterplant from western Asia. The initial introductions in the U.S. were in the 1870s in Cambridge, MA, followed by deliberate introduction into ponds near the Concord and Sudbury Rivers. This is now an invasive, habitat-destroying plant across many of the eastern states. On the Sudbury River, OARS (Organization for the Assabet, Sudbury and Concord Rivers) organizes annual plant pulling events. Volunteers in canoes hand-pull the surface-floating rosettes of leaves and nuts before the nuts mature and fall to the bottom. The infestation on the Sudbury River is particularly bad between the Fenwick Street and Saxonville dams, where the water surface can be more than 80% covered.