Well for comparison the sunflower has around 30% more base pairs in it's genome than the human genome, kentucky bluegrass has more than double, spruces have around 7x as many, pines have over 10x, but oak has less than a third.
So it's kind of all over the place. Even relatively similar plant species within the same family can have massively different genome sizes.
Chinese chestnuts have a comparatively small genome but they were only sequenced in the last 4 years and to my knowledge they are the only chestnut to have been sequenced.
“Polyploid organisms have more than two sets of homologous chromosomes. For example, humans have two sets of homologous chromosomes, meaning that a typical human will have 2 copies each of 23 different chromosomes, for a total of 46. Wheat on the other hand, while having only 7 distinct chromosomes, is considered a hexaploid and has 6 copies of each chromosome, for a total of 42.”
So it's kind of all over the place. Even relatively similar plant species within the same family can have massively different genome sizes.
Chinese chestnuts have a comparatively small genome but they were only sequenced in the last 4 years and to my knowledge they are the only chestnut to have been sequenced.