• Unique fossil: Seeds sprouting from an a

    From ScienceDaily@1:317/3 to All on Tue Nov 16 21:30:40 2021
    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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