Here, we present the descriptions of a new aphid species in the genus Pleotrichophorus Brner, 1930 (Hemiptera: Aphididae: Macrosiphini), found by Kenneth L. Hibbard, inspection supervisor for the Florida Department of Agriculture and Consumer Services, Division of Plant Industry. It is associated with Euthamia graminifolia (L.) Nutt. (Asteraceae) a native plant species in Florida, USA. Apterous and alate viviparous and oviparous females of Pleotrichophorus blackmani sp. n. are described and illustrated using light and scanning electron microscopy (SEM). SEM images of apterous viviparous female of Pleotrichophorus glandulosus (Kaltenbach, 1846), type species of the genus Pleotrichophorus, are given for the first time. Taxonomic notes are given, and an updated key to the apterae of the Euthamia-feeding aphids is provided. A multigene phylogenetic analyses of two New World Pleotrichophorus species places the genus in the tribe Macrosiphini sensu stricto. Pleotrichophorus glandulosus, the type species of the genus, was described from Germany. European specimens of P. glandulosus from France had similar molecular sequences to both Florida species, strongly suggesting that the new species belongs in Pleotrichophorus. COI and gnd sequence data indicate that P. blackmani sp. n. can be identified reliably by DNA barcodes.