Recalcitrant Seed Storage--the elephant in the forum

[A Happy Seedling]

No one wants to go near the tricky topic of storing recalcitrant seeds; we still need the information. If you have extra info about this, go ahead and post; I'll add it!
So...
[*] Recalcitrant seeds should NEVER be frozen! Ice crystals from the moisture they contain will permeate the seed and break its tissue, destroying its viability.
[*] They can supposedly be kept as cold as -10 degrees Celsius, as long as (somehow) they don't freeze, but I recommend only going as far as 3 Celsius (about 37 Fahrenheit; I use Fahrenheit but my info came from Celsius-using sites) to be safe.
[*] They can't be dried without losing their viability (but you already know this!)
[*] They lose viability, even wet, faster than orthodoxes

There you go: it's a start! We'll surely add more as we go.

[rainbowgardener]

I had never heard the term recalcitrant seeds, I guess since it seems to mainly apply to tropical plants that I am not familiar with, so I looked it up. For others in the same boat, here's what wiki says:

Recalcitrant seeds (subsequently known as Unorthodox seeds) are seeds that do not survive drying and freezing during ex-situ conservation and vice versa.[1] By and large, these seeds cannot resist the effects of drying or temperatures less than 10°C; thus, they cannot be stored for long periods like orthodox seeds because they can lose their viability. Plants that produce recalcitrant seeds include avocado, mango, mangosteen, lychee, cocoa, rubber tree, some horticultural trees,[2] and several plants used in traditional medicine such as species of Virola and Pentaclethra. Generally speaking, most tropical pioneer species have orthodox seeds but many climax species have recalcitrant or intermediate seeds

[imafan26]

You are right rainbow a lot of recalcitrant seeds are in the tropics. These are seeds that lose viability very fast and cannot be stored.

Chayote is recalcitrant -you have to plant the whole fruit. In fact it will sprout whether you plant it or not in a few days.
Mango
avocado
cocoa
Brazil nut
coconut
oak
loquat
lychee
rubber
mangosteen
algae and other aquatic plants
Most of these seeds must be planted while the fruit is still young and juicy. Once dessicated or frozen the embryo dies. Most of these have large seeds surrounded by a fleshy and juicy pulp and the seeds are viable when they are immature.
https://www.nsl.fs.fed.us/chapter%204.pdf

[A Happy Seedling]

Don't forget a lot of other tropicals and exotics! Like mamey sapote, and other sapotes, and many many other tropicals. Strange that a SQUASH (Chayote) is recalcitrant! I thought of mostly sweet, juicy tropicals. Ice cream bean is THE embodiment of the concept "recalcitrant seed", and I think mamey sapote and mango are the most iconic seeds. (Mamey seed is beautiful glossy black; when mine drops its seedcoat I'm keeping that coat!) And we all know the classic avocado pit and the hairy mango seed husk!

[imafan26]

There are a lot more. I don't like sapote a little sickly sticky sweet for me. Tamarind are also recalcitrant, by noting the number of dry pods under the trees and no seedling anywhere. Sour sop seeds have to be planted as soon as you spit them out, they really don't store well at all and they still take 4 months to germinate. Jaboticaba is another recalcitrant seed.

Other characteristics of recalcitrant seeds that are not noted by most people but are easy to guess at are
recalcitrant seeds take a long time to germinate... count the months, not the days except for some like chayote which will sprout still attached to the vine in a couple of weeks. I think the difference is in the rate of maturity. Chayote fruit grow really fast, if you don't pick them soon enough they get too large to eat in a few days. Most of the fruit trees take months for the fruit to develop. Avocados take nine months to mature on the tree to be edible. If you wait longer they will sprout on the tree as well.
Coconuts take about 2 years to germinate
Mango is relatively fast if you scarify and it will be up in less than a month. The really good thing is that you can eat the mango and just scrub and plant the seed. As long as you do it right away it will still grow. Don't try to keep it, it will turn dark brown, get soft and it is too late.
Most recalcitrant trees have a lot of 'fruit' drop but not a lot of seeds popping up under the tree. Mature and over mature seeds don't sprout.
Recalcitrant trees for the most part are relatively long lived for the tropics.
Except for coconut most of the whole fruit that is planted will rot if it gets too much water before the roots hit the ground. The seed comes with its own supply of water and nourishment until the roots hit the ground.

[A Happy Seedling]

A-a-aa! Tamarind seeds last a few months. I saved some in January and will plant in greenhouse now. Will try to germinate, see what works.