library(VennDiagram)

 BM1 <- c('Cistaceae', 'Oleaceae','Fagaceae','Rhamnaceae','Asteraceae','Asteraceae')
 BM2 <- c('Boraginaceae','Poaceae','Poaceae')
 BM3 <-  c('Poaceae','Asteraceae','Chenopodiaceae','Asteraceae','Poaceae','Solanaceae','Solanaceae','Asteraceae','Rubiaceae')
 BM4<- c('Amaranthaceae','Chenopodiaceae','Convolvulaceae','Convolvulaceae','Cucurbitaceae','Cucurbitaceae','Cucurbitaceae','Cucurbitaceae','Boraginaceae','Boraginaceae','Solanaceae')

 v2 <- venn.diagram(list(Oak=BM1, Wasteland=BM2,Edge=BM3, Crop=BM4),
               fill = c("red", "blue","green","purple"),
               alpha = c(0.5, 0.5, 0.5,0.5), cat.cex = 1.5, cex=1.5,
               filename=NULL)
grid.newpage()
grid.draw(v2)


 v2[[7]]$label  <- paste(setdiff(BM1,union(BM2,BM3)),collapse = "")
 inters <- intersect(BM1,intersect(BM2,BM3))
 v2[[8]]$label <- paste(setdiff(intersect(BM1,BM2), inters),collapse = "")
 v2[[9]]$label <- paste(setdiff(BM2,union(BM1,BM3)),collapse = "")
 v2[[10]]$label <- paste(setdiff(intersect(BM1,BM3), inters),collapse = "")
 v2[[11]]$label <- paste(ww[[1,5]], collapse = "")
 v2[[12]]$label <- paste(setdiff(intersect(BM3,BM2), inters),collapse = "")
 v2[[13]]$label <- paste(setdiff(BM3,union(BM1,BM2)),collapse = "")


grid.newpage()
grid.draw(v2)

library(VennDiagram)

BM1 <- c('Cistaceae', 'Oleaceae','Fagaceae','Rhamnaceae','Asteraceae','Asteraceae')
BM2 <- c('Boraginaceae','Poaceae','Poaceae')
BM3 <- c('Poaceae','Asteraceae','Chenopodiaceae','Asteraceae','Poaceae','Solanaceae','Solanaceae','Asteraceae','Rubiaceae')
BM4<- c('Amaranthaceae','Chenopodiaceae','Convolvulaceae','Convolvulaceae','Cucurbitaceae','Cucurbitaceae','Cucurbitaceae','Cucurbitaceae','Boraginaceae','Boraginaceae','Solanaceae')

lista_conjuntos <- list(Oak=BM1, Wasteland=BM2,Edge=BM3, Crop=BM4)

v2 <- venn.diagram(lista_conjuntos,
                   fill = c("red", "blue","green","purple"),
                   alpha = c(0.5, 0.5, 0.5,0.5), cat.cex = 1.5, cex=.8,
                   filename=NULL)

labels <- lapply(calculate.overlap(lista_conjuntos), function(x) {paste(unique(x), collapse='n')})

 tail(labels, 3)
$`a14`
[1] ""

$a1
[1] "Rubiaceae"

$a3
[1] "AmaranthaceaenConvolvulaceaenCucurbitaceae"

min(which(unlist(lapply(v2, function(x) {class(x)[[1]]}=="text"))))
[1] 9

for (x in names(labels)) {
    v2[[ start + as.integer(gsub("a", "",x)) ]]$label = labels[[x]]
}

grid.newpage()
grid.draw(v2)