Seriphidium herba-album and Tanacetum sinaicum are important medicinal plants belonging to family Asteraceae; covering large areas within St. Katherine protectorate wadies and mountains.  These plants are suffering from number of biotic stresses including plant galls (tumors) induced by the gall midge Rhopalomyia spp.. Permanent slides of galled and non-galled tissues were made in order to assess the anatomical induced effects in the host plants. Induction of a nutritive tissue surrounded by a storage tissue was recorded in both plants. A newly developed vascular tissue connecting gall tissues with the stem was formed in both plants. Formation of neo-vascularization within the gall tissue was a key feature within Tanacetum sinaicum galls. Induction of hairy non-glandular protective tissue was characteristics to Seriphidium herba-album galls. Despite sharing common anatomical features, galls induced in both plants were morphologically different. It was suggested that galls of both plants were induced by different Rhopalomyia species. More studies are needed to accurately identify the gall inducer species.