Malacothamnus ma·la·cot·hamnus uncommon noun 1. genus of shrubs or small trees: chaparral mallow Synonymsgenus Malacothamnus Related words Word family Malacothamnus fasciculatus Broader terms dilleniid dicot genus Parts Malvaceae Part of chaparral mallow WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.