All living horsetails are placed in the genus "Equisetum". The evolutionary distance between "Equisetum" and the Poales suggests that each evolved MLG independently. This gives them a jointed appearance superficially resembling the stems of some species of "Equisetum". This order consists of a single monotypic family, Equisetaceae, with one genus "Equisetum". All other "Equisetum" species are toxic. The crude cell extracts of all "Equisetum" species tested contain (MXE) activity. Other plants with similar life cycles include "Psilotum", "Lycopodium", "Selaginella" and "Equisetum". For the plant horsetail see Equisetum. "Equisetum" leaves are greatly reduced and usually non-photosynthetic. "Equisetum arvense" is toxic to stock, particularly horses. "Equisetum" has about 20 species. "Equisetum palustre" is poisonous to herbivorous animals, but not to humans. "Equisetum hyemale" has vertical jointed reed-like stalks of medium to dark green. "Equisetum palustre" is green from spring to autumn and grows spores from June to September. "Equisetum pratense" occurs in alluvial woods, thickets, mossy glades, and calcareous meadows.