Sentence:  Plant breeding is always a numbers game....The wild <WSD>species</WSD> we use are rich in genetic variation, and individual plants are highly heterozygous and do not breed true. In addition, we are looking for rare alleles, so the more plants we try, the better. 
Meaning of the word marked with <WSD> tags:  A rank in the classification of organisms, below genus and above subspecies; a taxon at that rank.