Rosaceae is divided into four subfamilies, mainly on the basis of how the fruit develops:
The rose is a rose
- Subfamily Rosoideae: Many small fruits, each of which is an achene or drupelet, and often the fleshy part of the fruit (e.g. strawberry) is the hypanthium or the stalk bearing the carpels.
- Subfamily Spiraeoideae: A non-fleshy fruit consisting of five capsules.
- Subfamily Maloideae: Five capsules (called "cores") in a fleshy endocarp, surrounded by the ripened stem tissue. This structure is called a "pome". Apple, pear, quince, hawthorn.
- Subfamily Amygdaloideae (or Prunoideae): A single drupe with a seam, two veins next to the seam, and one vein opposite the seam. Peach, almond, cherry.
and was always a rose;
But the theory now goes
That the apple's a rose,
And the pear is, and so's
The plum, I suppose.
You, my love, are a rose,
but were always a rose.
- - Robert Frost, "The Rose Family"
http://www.life.uiuc.edu/plantbio/260/Rosaceae/Rosehome.html as of 2002-05-29