I thought this is a simple question, but after some searching over the Internet, I just found several out-of-date databases like http://data.kew.org/cvalues/
There are several useful resources though: http://www.phytozome.net/ http://www.plantgdb.org/ But I did not find any direct information on genome size.
A workaround would be to download all the fasta files of chromosome sequences of these species and just look at the file size..
I'm just wondering is there any resources on plant genome size, or if not, an efficient way to get this information?
It's important to stress that most eukaryotic genome size estimates are based on total DNA weight per cell. So, there plenty more estimates besides those in NCBI and related.