Very interesting, William. I was under the impression that the "Pasco Giants" are the only known stable "long arm" form. Have you grown these plants from North Carolina and Alabama? I would love to see pictures.
Can the sterile plants really be considered D. capillaris? Schnell mentioned a location known to contain D. capillaris x intermedia in the second edition of _CPs of US and CAN_; isn't the likelihood of other such sites being in existence fairly high?
I'm also very interested in trading for seeds or plants from D. capillaris (and D. brevifolia!) locations...