Answer: There are so many plum varieties and hybrids, it's impossible for me to positively identify your plum. I checked several references, and found one that might fit the description:
'Elephant Heart': large, heart-shaped fruits, skin is first reddish and bronze-green, then turning to dark reddish purple when completely ripe. Dark purple-red, very juicy flesh.
I found this variety in a somewhat outdated catalog from:
Southmeadow Fruit Gardens
Lakeside, MI 49116
616-469-2865, Fax: 616-422-2411
The catalog doesn't state whether this variety needs a second tree to pollinate it, so you'll have to check with them if you decide to order it. Plums vary in whether or not they require cross-pollination. If this variety does need a pollinator, be sure to check with the nursery about an appropriate choice, since not all plums will pollinate each other effectively.
Regarding cross-pollination of fruit trees: Some types of fruit trees won't set fruit unless they are cross-pollinated, while others are self-fertile. Pollination requirements vary with fruit type, and even within classes--for example, some plums are self-pollinating, others are not. However, most fruit trees will produce a better crop if a compatible pollinator is growing nearby. One of the keys to compatibility is that the trees flower at the same time; also, some trees--certain pear varieties, for example--produce pollen that is incompatible with other pear varieties, so always seek advise from an experienced nurseryman.
I hope this helps!
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