Glendive Montana Trip #8
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Glendive, Montana Road Trip #8
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Part 8: Sierra Nevada & Amborella
© W.P. Armstrong 11 October 2011

Table Of Contents

  1. Snow-Covered Sierra Nevada & Fall Colors     
  2. A Liverwort In Creek Near The Walker River
  3. Amborella: Most Primitive Flowering Plant
    Side Trip To Huntington Botanical Garden

1. Snow-Covered Sierra Nevada & Fall Colors

Mono Lake & the snow-covered Sierra Nevada.

Mono Lake & the snow-covered White Mountains.

2. A Liverwort In Creek Near The Walker River

Liverwort in a creek near the Walker River north of Bridgeport. It resembles on-line images of the thalloid liverwort Conocephalum conicum. It has a well-marked hexagonal surface on the upper thallus. In the center of each hexagon is a minute pore. These features are barely visible in the above image. The plant was growing in shallow water of a marsh along a slow moving creek with dense population of Lemna trisulca.

Lemna trisulca (lower) and liverwort resembling Conocephalum conicum. Dense colonies of these plants were growing intermixed in the shallow water of a marsh along a creek near the Walker River (north of Bridgeport).

Highly magnified view of polygonal surface on the upper (dorsal) side of liverwort thallus. The polygons delineate the internal air chambers. In the center of each polygon is a rimmed pore. Each pore leads into an air chamber containing columns of photosynthetic cells and facilitates in gas exchange. Unlike the stomata of vascular plants which close in dry weather, the air pores of liverworts remain open all the time. Liverworts cannot control their water loss (transpiration) through the pores. They must live in shady, moist areas where they can imbibe water, and where there is sufficient water for their swimming sperm to reach the egg. Magnification 400x.

Close-up view of liverwort thallus. Minute disklike structure superficially resembles a gemma cup; however, except Conocephalum does not produce gemmae. Image taken with Nikon 1:1 macro lens.

  See Wayne's Word Bryophyte Page With More Liverwort Images  

3. Amborella: The Most Primitive Flowering Plant

A Side Trip To The Huntington Botanical Garden

On my return from the last leg of this trip, I was informed by horticulturist Dylan Hannon at Huntington Botanical Garden in San Marino that Amborella trichopoda was in full bloom. Amborella is the most primitive of all known flowering plants and its origin is placed on a sister clade with the first angiosperms. It belongs to the monotypic family Amborellacea, class Dicotyledoneae. Although considerable evidence has been compiled since the time of Darwin, the precise origin of flowering plants in the early Cretaceous (140 millon years ago) remains an enigma. Charles Darwin mentioned this controversy in 1879 when he referred to the origin of flowering plants as an "abominable mystery." There are at least four hypotheses to explain the origin of flowering plants (see Origin Of Flowering Plants on the Wayne's Word Evolution Page).

Molecular phylogenetic studies indicate that the first split within modern angiosperms is between a lineage that includes a single species (Amborella trichopoda) and all the rest of the extant angiosperm species. In other words, Amborella is monophyletic with all the rest of the angiosperms (see right cladogram: Origin of Amborella & Angiosperms). Amborella trichopoda is a rare flowering shrub that grows in the rain forest understory in New Caledonia. Unlike practially all other angiosperms, Amborella xylem has only tracheids, supporting the modern view that the first angiosperms lacked vessels. Amborella gametophytes are also unusual in having three, rather than two, synergid cells with the egg cell at the micropylar end (egg apparatus), hence a total of nine nuclei and eight cells in the embryo sac. According to W.E. Friedman (Nature 441, 2006), this extra cell in the egg apparatus could provide evidence of a critical link to the gymnospermous ancestors of flowering plants. The gametophyte of the vast majority of angiosperms has three cells in the egg apparatus, and a total of seven cells and eight nuclei in the embryo sac.
Origin of Amborella & Angiosperms.

  Origin Of Flowering Plants On Evolution Page  

Water Lily (Nyphaea odorata)
Amborella trichopoda (above): A rare, sprawling, understory shrub from New Caledonia, and the most primitive living flowering plant. It belongs to the monotypic family Amborellaceae in the monotypic order Amborellales. Most authorities consider it to be the living descendent of a line of primitive flowering plants without vessels that diverged near the base of the main clade of vessel-bearing angiosperms about 130 million years ago. The younger growth (inset) has bright green, shiny leaves. The flowers have many tepals (perianth parts not differentiated into calyx & corolla) and numerous stamens. They are similar in appearance to miniature versions of the closely-related water lily clade (order Nymphaeales), see left image.

Suggested phylogenetic relationship between Amborella trichopoda and other extant genera of gymnosperms and angiosperms. Amborella is of great interest to plant taxonomists because molecular phylogenetic analyses consistently place it at or near the base of the flowering plant lineage (phylogenetic tree). That is, it represents a line of flowering plants that diverged very early (about 130 million years ago) from all the other extant species of angiosperms. Comparing characteristics of this basal aniosperm with other flowering plants and fossils may help us figure out how flowers first appeared--what Darwin called the "abominable mystery." Cladogram courtesy of Wikipedia Comnmons.

San Diego Botanic Garden 28 July 2013

Underside of flowering branch of male Amborella trichopoda.

Close-up view of male (staminate) flowers of Amborella trichopoda. Each flower is aprroximately 4 to 5 mm in diameter with a dozen or more bract-like tepals (perianth segments undifferentiated into petals & sepals). The flowers have a dozen or more spirally arranged stamens, which become progressively smaller toward the center.