Goniothalamus maewongensis is a species of plant in the family Annonaceae. It is native to Thailand.[1] Richard M.K. Saunders and Piya Chalermglin, who first formally described the species, named it after the Mae Wong National Park in Thailand where the type specimen was collected.[2]
It is a tree reaching 8 meters in height. Its oblong, papery leaves are 19.5-25.5 by 5-7 centimeters with tips that taper to a point and wedge-shaped or pointed bases. Its leaves have smooth upper sides and lightly hairy undersides. The leaves have 13-15 pairs of secondary veins emanating from their midribs. Its petioles are 7-14 by 1.7-2.4 millimeters and hairless or sparsely hairy. Its solitary flowers are axillary and droop downwards. Its flowers are on densely hairy pedicels that are 12-14 by 1.7-2 millimeter. The pedicels have up to 5 bracts. It has 3 light-yellow, oval to triangular sepals, 5 by 5 millimeters, with smooth inner surfaces and lightly hairy outer surfaces. The margins of the sepals are fuse at their base, and they curve back on themselves when mature. It has 6 petals in two rows of three. Its 3 light-yellow, oval shaped outer petals are 19 by 15 millimeters, and densely hairy on both surfaces. Its inner petals are 9-13 by 6.5-7 millimeters, densely hairy on both surfaces and yellow with pink highlights. Its flowers have up to 200 stamens that are 2.3-2.5 by 0.6-0.7 millimeters. Its flowers have up to 20 carpels with ovaries that are 2.7-2.9 by 0.3-.05 millimeters. The ovaries are bald, with the exception of a line of gold-colored hairs. The stigma and hairless style together are 3.2-3.6 millimeters long. The stigma are spindle-shaped, hairless and have warty appearance. Clusters of fruit are born on 10-18 by 2.7-2.8 millimeters hairy pedicels. The round to elliptical, green-colored fruit are 21-35 by 16-26 millimeters with smooth or slightly wrinkly surfaces. Each fruit is attached by a 1 by 2.3 millimeter hairless stipe. Each fruit has 1-4 elliptical, wrinkly, brown seeds that are 18-21 by 18-19 millimeters and sparsely covered in hairs.[2]
The pollen of G. maewongensis is shed as permanent tetrads.[2]
It has been observed growing in mountainous rainforests at altitudes of 1300 meters.[2]
Bioactive molecules extracted from its bark and leaves have been reported to have cytotoxic activity in tests with cultured human cancer cells.[3]