Giant Hogweed vs Cow Parsnip

Today's Commercial Appeal featured an article by Felder Rushing on Poisonous Giant Hogweed.  Here's his picture:

And here's a picture of me beside a similar plant in my neighborhood in North Carolina:

My neighbors and I had identified this plant as Cow Parsnip, but when I read Felder's article, I wasn't so sure.  So I did some research.

Cow Parsnip is Heracleum maximum; Giant Hogweed is Heracleum mantegazzinum, different species of the same genus.  The sap of both species will cause phytophotodermititus (severe skin inflammation), but the Hogweed sap is much more toxic.  So how to tell them apart?

The keys to Giant Hogweed identification are:

• large plant, often over 8 feet high (when mature)
• flowers in umbel shape, larger than 6 inches in diameter
• flowers have more than 50 rays
• hollow stems are between 1-3 inches in diameter
• stems have stiff white bristles
• stems have spots or blotching, red or purple in colour
• large, lobed leaves up to 3 feet in size
• leaves compounded in three

So how does my specimen stack up?  

Height is over 8 feet:  I'm about 5.5 feet tall, and the plant is in a small depression, so its base is below where I'm standing.

Umbel flowers, greater than 6 inches - check.

Here's a closeup of the stem:

The diameter of this one is over an inch, and you can see the red splotching.  I can't see any bristles, though, and I don't remember whether there were any or not.

Umbels have more than 50 rays - here's another closeup:

What do you think?  Looks like a bunch to me.  But here's a picture from the Wikipedia entry for Giant Hogweed:

So I don't know.  

Another difference is in the seed shape.  Cow parsnip seeds are heart-shaped; giant hogweed seeds are oval.

I'll be in NC in a couple of weeks and I'll do some closer inspection and maybe come to a more definitive answer.