 The multi @-@ genus approach is based solely on the structure of the male flowers ; no other characters could be consistently associated with one genus or another . Four of the genera — <unk> ( in a narrow sense ) , <unk> , <unk> and <unk> — correspond to four different types of male flowers found within the genus . However , a few species have flowers that are intermediate between these four types , including A. <unk> ( which <unk> placed in its own genus , <unk> ) and this has been used as an argument for the single @-@ genus approach . In addition , there are several hybrids between species that would be considered different genera under <unk> 's five @-@ genus system , which has also been used as an argument for placing them in a single genus . In 2009 Alan <unk> and colleagues published a molecular phylogeny of the <unk> which found that some species placed in <unk> were actually more closely related to species placed in <unk> than they were to other members of that genus ( if the five @-@ genus approach was used ) , while A. <unk> , placed in <unk> by <unk> , was actually a sister to both <unk> and <unk> . 
