Crownshaft

Lower portion or base of the leaves on some pinnate palms, where they wrap around the trunk and attach to form a smooth, often buldging area immediately above the woody trunk. As the oldest fronds dry up, unwrap and pull away from the trunk, they form the distinct rings or leafbase scars seen on many palms. These are often refered to as self cleaning palms.

Crownshaft detail of Hedescepy canturburyana. Old leaf base scars visible on trunk

Crownshaft of Burretiokentia vielardia

Another example of crownshaft: Roystonea regia

Wodyetia bifurcata, A popular crownshafted palm