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The
pistachio is a broad, bushy, deciduous tree which grows slowly to a height and
spread of 25 to 30 feet, with one or several trunks. The trees are inclined to
spread and droop, and may initially need staking. Their open habit and attractive
foliage make them valuable ornamentals. Under favorable conditions pistachio trees
live and produce for centuries. The large, grayish leaves have 3 to 5 roundest,
2 to 4 inch-long leaflets. Pistachios
are dioeciously with male and female flowers on separate trees. Male and female
trees must be present for fruit to set, or a branch from a male tree may be grafted
on a female tree. The small, brownish green flowers are without petals and borne
on maxillary racemes or panicles in early summer. Wind carries the pollen from
the male to the female flowers. The reddish, wrinkled fruits are borne in heavy
clusters somewhat like grapes. Although known as a nut, the fruit of the pistachio
is botanically a drupe, the edible portion of which is the seed. The oblong kernel
is about 1 inch in length and 1/2 inch in diameter and protected by a thin, ivory-colored,
bony shell Normally the shells split longitudinally along their sutures when mature.
Under unfavorable conditions during nut growth, the shells may not split open.
The color of the kernel varies from yellowish through shades of green, which
extends throughout the kernel. In general the deeper the shade of green, the more
the nuts are esteemed. Pistachio nuts are rich in oil, with an average content
of about 55%. The trees begin bearing in 5 to 8 years, but full bearing
is not attained until the 15th or 20th year. Pistachios tend toward biennial bearing,
producing heavy crop one year followed by little or none the next. Production
of nuts is also influenced by drought, excessive rain, heat or cold and high winds.
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