Lessoniaceae

Lessoniaceae are a family of kelp. They are the largest of all algae, and are characterized by the single blade splitting into two. Some species have pneumatocysts at the base of their blades.

Taxonomy
The genera of this family can be hard to tell apart, but can be differentiated based on their habitat and the position of their pneumatocysts.
 * Lessonia is relatively short, with multiple stipes, inhabiting intertidal or low tidal areas. This genus has no pneumatocysts.
 * Macrocystis is the largest of the kelps, and has multiple stipes and multiple pneumatocysts on each stipe, with one blade each.
 * Nereocystis has a single stipe, and a single pneumatocyst with multiple blades.
 * Pelagophycus is much like Nereocystis, but has two separate stalks emerging from the pneumatocyst, from which sprout the blades, earning it its nickname of "elk kelp."
 * Postelsia is intertidal, and for most of the time is exposed to the air. It has a single upright stipe, no pneumatocyst, and multiple hanging blades.

Other genera are:
 * Dictyoneurum
 * Lessoniopsis

Distribution
The distribution of Lessoniaceae includes the northeastern Pacific Ocean and southern Australian coasts.