Unique fossil: Seeds sprouting from an amber-encased pine cone

Date:
November 16, 2021
Source:
Oregon State University
Summary:
New research has uncovered the first fossil evidence of a rare
botanical condition known as precocious germination in which seeds
sprout before leaving the fruit.



FULL STORY ========================================================================== Oregon State University research has uncovered the first fossil evidence
of a rare botanical condition known as precocious germination in which
seeds sprout before leaving the fruit.


==========================================================================
In a paper published in Historical Biology, George Poinar Jr. of the
Oregon State College of Science describes a pine cone, approximately 40
million years old, encased in Baltic amber from which several embryonic
stems are emerging.

"Crucial to the development of all plants, seed germination typically
occurs in the ground after a seed has fallen," said Poinar, an
international expert in using plant and animal life forms preserved in
amber to learn about the biology and ecology of the distant past. "We
tend to associate viviparity -- embryonic development while still inside
the parent -- with animals and forget that it does sometimes occur in
plants." Most typically, by far, those occurrences involve angiosperms,
Poinar said.

Angiosperms, which directly or indirectly provide most of the food people
eat, have flowers and produce seeds enclosed in fruit.

"Seed germination in fruits is fairly common in plants that lack
seed dormancy, like tomatoes, peppers and grapefruit, and it happens
for a variety of reasons," he said. "But it's rare in gymnosperms."
Gymnosperms such as conifers produce "naked," or non-enclosed, seeds.

Precocious germination in pine cones is so rare that only one naturally occurring example of this condition, from 1965, has been described in
the scientific literature, Poinar said.



========================================================================== "That's part of what makes this discovery so intriguing, even beyond
that it's the first fossil record of plant viviparity involving seed germination," he said. "I find it fascinating that the seeds in this
small pine cone could start to germinate inside the cone and the sprouts
could grow out so far before they perished in the resin." At the sprouts'
tips are needle clusters, some in bundles of five, associating the fossil
with the extinct pine species Pinus cembrifolia, which was previously
described from Baltic amber, Poinar said.

Pine cones in Baltic amber are not commonly found, he added. The ones
that do appear are prized by collectors and because the cones' scales
are hard, they're usually very well preserved and appear lifelike.

Viviparity in plants typically shows up in one of two ways, Poinar said.

Precocious germination is the more common of the two, the other being vegetative viviparity, such as when a bulbil emerges directly from the
flower head of a parent plant.

"In the case of seed viviparity in this fossil, the seeds produced
embryonic stems that are quite evident in the amber," he said. "Whether
those stems, known as hypocotyls, appeared before the cone became
encased in amber is unclear. However, based on their position, it appears
that some growth, if not most, occurred after the pine cone fell into
the resin.

"Often some activity occurs after creatures are entombed in resin,
such as entrapped insects depositing eggs," Poinar said. "Also, insect parasites sometimes flee their hosts into the resin after the latter
become trapped. In the case of the pine cone, the cuticle covering the
exposed portions of the shoots could have protected them from rapid
entrance of the resin's natural fixatives." Research on viviparity
in extant gymnosperms suggests the condition could be linked to winter
frosts. Light frosts would have been possible if the Baltic amber forest
had a humid, warm-temperate environment as has been posited, Poinar said.

"This is the first fossil record of seed viviparity in plants
but this condition probably occurred quite a bit earlier than
this Eocene record," he said. "There's no reason why vegetative
viviparity couldn't have occurred hundreds of millions of years
ago in ancient spore-bearing plants like ferns and lycopods." ========================================================================== Story Source: Materials provided by Oregon_State_University. Original
written by Steve Lundeberg. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. George Poinar. Precocious germination of a pine cone in Eocene
Baltic
amber. Historical Biology, 2021; 1 DOI:
10.1080/08912963.2021.2001808 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211116131739.htm

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