"God Almighty first planted a garden. And, indeed, it is the purest of human
pleasures."
-- Francis Bacon, Essays : Of Gardens
What is a Pinetum ?
"We first knew you a feeble
plant which wanted a little earth whereupon to grow. We gave it
to you, and afterward when we could have trod you under our feet,
we watered and protected you; and now you have grown to be a
mighty tree, whose top reaches the clouds, and whose branches
overspread the whole land, whilst we, who were the tall pine of
the forest, have become a feeble plant and need your protection."
-- Sagoyewatha, statement c.1792
The Latin word PINETUM meant pine grove and that is still very close to today's most precise definition. A pinetum is a grove or plantation where pine trees are cultivated, particularly for scientific, educational &/or esthetic purposes. It is a specialized type of arboretum -- a place where many kinds of trees are grown for the same purposes. (Latin: arbor = tree; pinus = pine tree).
Most tree collections are referred to as an arboretum or botanic garden, no matter what kind of trees were grown there and the word pinetum is seldom used. And even the few tree collections that are called "_________ Pinetum" almost always have more genera than just pines. The most famous of the world's pinetums (the Romans would have said the plural is pineta) is the Bedgebury National Pinetum in County Kent, England and it contains not only pine trees. Most of the non-pines there are other types of conifers such as spruce, fir, Douglas fir, larch, cypress, false cypress, dawn redwood, incense cedar, sequoia, etc. and even a few non-conifers such as maples, sweet gum, cherry are found at Bedgebury.
So the definition of pinetum has been blurred by modern (mis-?) use of the term or by (mis-?) planting of non-pines. A fair compromise definition of pinetum would be an arboretum with predominantly conifers.