epigeal vs. hypogeal(?)

sequoia_stiffy(9)December 13, 2007

Maybe somebody can help me. I'm confused as to what exactly is the difference between these terms in reference to seed germination. When someone says that "germination is epigeal", does that mean that the seed does not need to be buried to germinate, and thus hypogeal means that the seed does need some depth below the surface to germinate or am i thinking about this in the wrong way?

Also, I read something about how hypogeal refers to temperature changes that are needed to induce germination. It's confusing the hell out of me really. If a redwood seed is "epigeal", what in the hell does that mean exactly?

Also, I checked on a dawn redwood seed that I planted from gathered seed a few weeks ago (along with about a hundred other dawn redwood seeds that didn't germinate). It is just bursting it's seed coat and sending the tiny tip of what is to be a root down into the soil. I oriented it a bit with the tip of a knife (very gently) and covered it with a small bit of rich black soil, only about a mm though. I am guessing this will help it's root establish.

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Epigeal means the germinating seedling lifts its cotyledons out of the soil so they can turn green and photosynthesize; most conifers do this.

Hypogeal means the cotyledons stay in the soil, acting as a food store for the seedling but not doing any photosynthesis. Acorns and walnuts are the usual examples cited; it is rare in conifers; examples include Araucaria araucana and Torreya californica.

Nothing much to do with depth of seed planting!


Here is a link that might be useful: Useful glossary

    Bookmark   December 13, 2007 at 5:10AM
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davidrt28 (zone 7)

Years ago I bought some Araucaria angustifolia seeds from the good people at Chiltern. I'm not sure they were correctly labeled, now, because the resulting plants DID NOT resembled what I bought last winter as A.a. from Sheffield Seeds. (which, in spite of the name, is in the US)

But let me tell you...these had a bizarre germinating which I believe was hypogeal. The nut opened, and a slimy red "umbilical cord" that was disturbingly non-root like emerged and grew about 3-4" long for most of them. Then its distal end started thickening up, eventually forming a little rootlet with bark that was like miniaturized conifer bark. Then the slimy connection rotted away, separating from the mother ship. The rootlet (cotyledon, presumably) sat there for a few months until it got hot here in the summer and I set them out. THEN they sprouted with a green top.

The green tops I have now are not scimitar-sharp as the ones from Chiltern had been, so I'm not really sure how to type them. I'm thinking the Chiltern seeds were one of the sharp Australian species, or just Araucaria araucana, however they were very heat resistant which suggests the former to me. Nor was there evidence that the Sheffield seeds went through the ridiculous germination process, tho I didn't scrutinize them as closely. (the Chiltern seeds were germinated in transparent sport drink bottles, allowing me to see what was going on, in some cases, last winter's batch from Sheffield in typical pots.) Also as specialists in Tree seed, I slightly trust Sheffield more in this area than Chiltern.

In neither case did I get good germination, only around 20%. I sold the 3 which I thought were Paranas to a crazy 6'7 Brazilian guy in NYC who drove all the way down to the DC area, in what I'll always wonder might have been a stolen car, to get them. He was convinced they would survived the winters there, I was selling them because I was sure they were in fact not zn 7 hardy, and in the years after germinating them I gave up on sending plants to my relatives who live at Virginia Beach because they kept losing things they should have been able to not kill. I told him not to plant them out, he did, in November(!) and NYC promptly had it's coldest winter in 20 years. ANY Araucaria species they were would have died, so I don't feel bad that now they prove to be mislabeled.

    Bookmark   December 13, 2007 at 4:25PM
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yeah, but my question continues...in the case of hypogeal germination (oak, etc.) how does the course of germination go, if the cotyledons don't elevate above the soil line and start photosynthesizing? And, does "cotyledon" refer to the "leaves" or the carbohydrate-filled bulk of the seed?

And, what are the steps of hypogeal germination, usually? First the root sends down, the cotyledons remain below soil level, and then the initial shoot/apical meristem shoots up, and then photosynthesizing leaves emerge from that, or what?

thanks so much by the way for taking the time to respond to this. I'm not a botany student at all, I'm just fascinated by this stuff and would have a bit harder of a time learning it were you all not to take the time to answer my questions directly. I definitely appreciate it.

    Bookmark   December 13, 2007 at 11:32PM
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davidrt28 (zone 7)

Well, I think what I narrated pretty much summed it up. I'm sure someone else will add something eventually. In the case of hypogeal germination the cotyledon is the carbohydrate filled "nodule" that develops from the nut/seed.

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Hypogeal means "underground".

* In botany, a seed is described as hypogeal when the cotyledons of the germinating seed remain non-photosynthetic, inside the seed shell, and below ground. The converse, where the cotyledons expand, throw off the seed shell and become photosynthetic above the ground, is epigeal.

    Bookmark   December 13, 2007 at 11:44PM
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Fledgeling_(4b SD)

Cotyledon, or seed leaves, are not considered the true leaves- ever notice on how some plants first set of leaves look nothing like their second set? ThatÂs the Epigeal plantsÂs Cotyledon.

    Bookmark   December 14, 2007 at 12:53PM
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Fledgeling_(4b SD)

before anyone says, seed leaves are not true leaves... yeh yeh

    Bookmark   December 14, 2007 at 1:52PM
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Fledgeling_(4b SD)

looks like i said that already. I am not not with it today, understand.


    Bookmark   December 14, 2007 at 1:55PM
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