doubtful species

基本解释

Taxus L. is a problematic genus, not only its species are discouragingly similar, but also its family circumscription are still doubtful.
红豆杉种属的问题，不但它的种类惊人地相似，而且其科的界限也非常模糊。
Given these pressures, and additional ones affecting other animals, it's doubtful that most mammal species will experience much of an overall growth spurt anytime soon.
在这些压力以及以及其它一些因素的作用下，大多数哺乳动物很难在短时间内出现体型上的巨大变化。
There are 51 species of the Gasteromycetes, in Shaanxi Province, including 2 doubtful species and 13 new records of Shaanxi Province, belonging to 19 Genus, 9 Families and 6 Orders.
本文报道了产于陕西省的腹菌纲真菌51种，其中包括2个疑难种和13个省内新记录种，隶属于6目、9科19属。