In article ,
wrote...

MMMavocado schreef
Avocado is a one-seeded berry. The papery membrane surrounding the
cotyledons is seedcoat. In the Mexican (Persea americana ssp. drymifolia)
and Guatemalan (P. americana ssp. nubigena) races, there is a single
seedcoat. In the West Indian race (P. americana ssp. americana), the coat is
separated into two distinct layers. But I've never heard anyone suggest
that the outer one is endocarp.

+ + +
Thank you!
Well, Mel, it is official now ...

I wasn't quite completely convinced by the above, since I'd seen
some equally authoritative-sounding [for all that's worth!]
statements elsewhere that conflicted. [But see below for strong
support.]

I'd hesitated at first because I'd vaguely remembered reading somewhere
that avocados actually varied as to whether there was an appreciable
development of a hard endocarp [possibly the same differences pointed
to above?], and thus would vary as to whether the fruit would be
classified as a drupe or as a 1-seeded berry. I then checked briefly,
and initially didn't find anyone calling the fruit a berry, but did
find several calling it a drupe:

http://www.csdl.tamu.edu/FLORA/Wilson/pp/f97/fruits.htm or
http://www.csdl.tamu.edu/FLORA/Wilso...u98/fruits.htm

"II. Other fruits and fruit-like structures:
3. DRUPE: Single carpel, single-seeded, pericarp tissue
differentiated into THREE layers: EXOCARP, MESOCARP,
ENDOCARP:
Peach - exocarp with fuzz
Nectarine and Plum - exocarp without fuzz
Almond - exocarp/mesocarp removed, just PYRENE [=endocarp
and seed]
Avocado - endocarp VERY thin
Coconut - mesocarp fibrous ,[dispersal], testa thin,
endosperm both solid [meat] and liquid [milk]
Raspberry - an AGGREGATE (separate ovaries of one flower
joined together) of small drupes [druplets]"
[...]

"TAXA EXAMINED - FRUIT LAB
LOCAL NAME GENUS SPECIES FAMILY CLASS FRUIT TYPE Carpel#
[...]
Avocado Persea americana Lauraceae Dicot Drupe 1"

http://www.csdl.tamu.edu/FLORA/Wilso...g/laupage1.htm

"The Magnoliidae
Family Overview - The Laurales
Lauraceae - the Laurel Family

The typical fruit type for the family - a drupe - is encountered with
the avocado (Persea americana) - the exocarp is peeled, the mesocarp
is fleshy, and the endocarp is reduced to a thin, brown covering of
the avocado seed."

http://flora.huh.harvard.edu:8080/fl...taxon_id=10479

"5. Lauraceae Jussieu
Laurel Family
[..]

Fruits drupes, drupe borne on pedicel with or without persistent
tepals at base, or seated in ± deeplycup-shaped receptacle (cupule),
or enclosed in accrescent floral tube. Seed 1; endosperm absent."

[...]

"8. Persea Miller, Gard. Dict. Abr. ed. 4. 1754.
[...]

Drupe dark blue to black, nearly globose, borne on pedicel with tepals
persistent at base; cupule absent."

http://pas.byu.edu/AgHrt100/avocado.htm

"The fruit is a drupe, having a stony endocarp."

But the "berry" description is gaining strong support:

http://www.cas.muohio.edu/~meicenrd/...logy/dln11.htm

Lauraceae (Laurel Family)
[...]
"III. Fruit
A. 1-seeded berry or drupe"

http://www.botgard.ucla.edu/html/bot...sea/index.html

"This berry is truly unusual, not only because it is oily, not sweet,
but also because it never softens while still on the tree, where it
remains hard and continues to grow.

[...]

The peel or rind (exocarp) consists of an epidermis with a cuticle,
but in the warty fruits, the epidermis is replaced with cork from a
cork cambium. The warts or bumps are airy zones in the cork called
lenticels. Beneath this are several layers of cells, the innermost
ones being sclerenchyma. The thick, green mesocarp is composed of
millions of small parenchyma cells, some that are specialized for oil
storage and others that have smaller amounts of oils. The endocarp
consists of several layers of thin-walled cells. In the center, the
seed has a double seed coat, two cotyledons rich in starch, and a
relatively small embryo."

http://www.cabi-publishing.org/books...1993575Ch2.pdf

Seems like a nice botanical treatment of the avocado.

["p. 16" (= 2nd page of the link)]:

"Fruit small, globose to large fleshy, obovoid one-seeded berry in
subgenus _Persea_."

[p. 30]

"The avocado fruit is botanically a one-seeded berry (Fig. 2.3f),
and is very variable in size (50 g to nearly 2 kg), shape (round,
oval, pyriform), rind characteristics (thickness, surface features,
colour), flesh, and seed characteristics (size, tightness in cavity,
etc.). Cummings and Schroeder (1942) described basic fruit anatomy.

[...]

The innermost flesh is a rather indistinct endocarp, made up of a
few rows of smaller, more flattened parenchyma cells. It is botanically
incorrect to refer to the flesh as a mesocarp, as by definition the
flesh of a berry fruit comprises mesocarp plus endocarp."

[p 32]

"The role of previously unreported tissues in avocado fruit development
has been outlined by Steyn et al. (1993) they not that the vascularized
part of the seed coat is actually a pachychalaza, with the testa (the
contribution of the integuments) representing only a very small
non-vascularized portion."

refs cited above:

Cummings, K and Schroeder, C. A. 1942. Anatomy of the avocado fruit.
California Avocado SocietyYearbook 1942, 56-64.

Steyn, E. M. A., Robbertse, P. J., and D. Smith. 1993. An anatomical
study of ovary-to-cuke development in consistently low-producing trees
of the "Fuerte" avocado (Persea americana Mill.) with special reference
to seed abortion. Sexual Plant Reproduction 6: 87-97.

cheers