Newt - first of all, a most humble apology for the mistaken gender. This, like planting cantelopes next to watermelons, will not happen again.
Not to fret, it happens all the time. Most folks think of that Gingrich guy when they see my name. 
...this evil weed is now removed and thrown on the pile of cut branches going to our local organic dump.
Organic dump? That's fantastic that you have such a wonderful resource. If you have the space, consider starting a compost pile so you can make your own compost.
Quick question: what's a good resource of indentifying plants for a novice like myself?
This won't be a quick answer as I need some clarification and need to explain how I found the imposter. I'm wondering if you want to id weeds or garden plants or both as I have several sites I use. Many weeds are geographic specific, so it would help to know where you live to see if I can find you a site to id weeds.
Now to explain how I found your imposter. I googled with the term: watermelon plants and clicked on 'Images' to see the similarities. I had never seen one with thorns, and none of the pics I turned up showed any either, so I then searched with the term: watermelon plants thorns. That's how I found the site that listed the buffalobur as an imposter. 
Then great news: we're expecting! I counted 8 little baby tomatoes on my grown from seed beefsteak! Ah, I'm such a proud parent!!!!!
Not much can compete with the taste of a sun warmed tomato picked right in the garden and eaten there imo! 
You are so very welcome! Let me know what type of sites you want for reference and what state you are in if you are in the US.
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.