M. grandis may refer to: * Meconopsis grandis, the blue Poppy, a flowering plant found in Bhutan * , a very small ectparasitic sea snail species in the genus Melanella * Melanodexia grandis, a fly species in the genus Melanodexia * Menegazzia grandis, a lichen species found in Australia * , a spider species in the genus Mexitlia found in Mexico * Millettia grandis, a legume species found in South Africa * Miohippus grandis, a prehistoric horse species found in now North America that lived from the late Eocene to early Miocene * , a spider species in the genus Moneta endemic to India * Mullerornis grandis, an extinct elephant bird species found in Madagascar