I ran across a plant-themed black and white photography contest hosted by 
Hopefully I'm entering the contest correctly. :-)
This is the apple that I'm eating today. It's a homely little thing -- far from the Red Delicious that we've been acculturated to think of as normal, but this came off a tree in my coworker's yard last week and while it's a little tart and tannic , I think it's a sort of lovely form.
I love the little plants, mosses, and lichens that grow in unlikely places. A few weeks ago, I'd climbed down into a crack in the rock plate we were walking on to take several pictures of these and I found this tree. It's a larger subject than I'm usually after, but I decided to get it. I was lining up the shot when my daughter, Kivi, jumped across the narrow part of the crack and walked through my background. It was kind of neat so I had her come back and plant her foot there for a second while I took a couple shots. Maybe I wish she'd been a little to the right for contrast behind the seedling's trunk, but it's still a nice shot.
This orchid sits on my desk. It was a Mother's Day gift to my wife from out son and daughter-in-law two years ago. It lived at our house for the summer, but we don't really have the right widows for indoor plants so it went to work with me (where I have huge windows). This is looking down at the plant's aerial roots with the central stem and several leaf-bases in the upper right.
Make sure you look at the photos other people are posting for this, some of them are amazing!