Mitrephora williamsii is a species of plant in the family Annonaceae. It is native to The Philippines.[1] Charles Budd Robinson, the Canadian botanist who first formally described the species, named it after Robert Statham Williams who collected the specimen that Robinson examined.[2]
It is a tree reaching 12 meters in height. Its oval leaves are 20-32 by 7–11.5 centimeters and come to a point at their tips. The leaves are smooth and shiny green on their upper surfaces while their undersides are brown-green and slightly hairy. The leaves have 20-25 pairs of secondary veins emanating from their midribs. Its petioles are 12-18 by 2.5-4 millimeters. Its fragrant flowers are red and yellow and are arranged in cymes opposite the leaves. Each flower is on a hairy pedicel 5-8 millimeters long. Its flowers have 3, oval-shaped sepals, 5-6 millimeters long, that come to a point at their tip. Its 6 petals are arranged in two rows of 3. The outer petals are 13-15 by 9-10 millimeters, hairy on their outer surface and smooth inside. The inner petals have a 10 by 2 millimeter claw below a 6-7 by 7.5 millimeter hood-shaped blade which is hairy on its inner surface. It has approximately 200-250 stamens that are 0.8-1 millimeter long.[3]
The pollen of M. williamsii is shed as permanent tetrads.[4]
It has been observed growing in low elevation forests.[5]