From the 2010 USABO Semi:
In plant systematics, three lines of evidence may be useful in determining relationships; xylotomical (wood anatomy), embryological and palynological. Match these three with the level for which they are most useful.
The options for the levels were order, family, and genus. The answers matched xylotomy to genus, embryology to order and family, and palynological to genus, but if anybody could provide some examples to explain that would be great. Thanks!