alligator-pear avocado avocado-pear butter-pear climacteric-fruit cultivar cut fertility-fruit firm flesh food fruit Fuerte-variety green guacamole healthy large-berry large-seed nutritious ovate pear-shaped perennials persea-americana ripe section smooth soft tree wrinkled alligator pear avocado pear black butter pear climacteric fruit egg-shaped fertility fruit Hass variety large berry large seed pebbled skin persea americana rough pebbled-skin kernel seed green-skinned hard unripened