Lecture Notes Review - Plant Biology

Mosses and Ferns: Characteristics and Ancient History

Mosses: Characteristics and Uses

Mosses are characterized by their low-lying growth habit, which necessitates direct absorption of moisture from their environment. The prominent, green, carpet-like part of a moss plant is the gametophyte, which is the dominant generation in mosses. When a moss reproduces, it produces a sporophyte, which emerges as a small stalk-like structure, releasing spores before eventually detaching. Medically, some mosses possess antiseptic properties, making them useful in various applications.

Ferns: Structure, Reproduction, and Vascular Tissue

Ferns manifest as larger plants compared to mosses, often featuring large leaves known as fronds, which consist of smaller leaflets. In ferns, the dominant generation is the sporophyte, not the gametophyte, unlike mosses. The sporophyte is the plant that produces spores, while the gametophyte is the plant that produces gametes. While the gametophyte is dominant and visible in mosses, the gametophyte of ferns and most other plants is non-dominant and often microscopic.

Vascular Tissue and Ancient Plant Size

The development of vascular tissue was a significant evolutionary advancement that allowed ancient plants, including ferns, to grow to immense sizes. This tissue facilitated the efficient transport of water and nutrients throughout the plant body, enabling greater height and structural integrity. At a time when gymnosperms and angiosperms had not yet evolved, plants like club mosses, tree ferns, and horsetails were the most adapted flora on Earth, reaching sizes comparable to modern trees. This period was also characterized by higher atmospheric carbon levels, which generally contribute to larger plant growth. Fossilized remains of these ancient plants form what we now know as coal, a fossil fuel.

Distinction Between Gametophyte and Sporophyte

To clarify, a gametophyte is the plant generation responsible for producing gametes (reproductive cells), while a sporophyte is the plant generation responsible for producing spores. In mosses, the gametophyte is the large, visible, dominant part. In all other plant groups discussed, including ferns, gymnosperms, and angiosperms, the sporophyte is the dominant generation, and the gametophyte is typically much smaller, often microscopic.

Giant Ancient Flora Reconstructions

Artist renditions based on fossilized remains depict ancient landscapes dominated by colossal versions of plants that are much smaller today. For example, ancient club mosses, which are now typically only a few inches high, once grew into massive trees. Similarly, tree ferns and horsetails were significantly larger in prehistoric times. With the evolution of more adapted plants like gymnosperms and angiosperms, these earlier plant forms became less dominant and typically smaller.

Sequoia National Park and Giant Trees

Sequoia National Park in California is renowned for its towering trees, including the famous giant sequoias. The park is home to Mount Whitney, the tallest peak in America, standing at 15,000 feet. A notable feature is the Giant Tunnel Log, a drive-through tree. The park's most famous resident is General Sherman, one of the largest living organisms on Earth. General Sherman is estimated to be over 2,000 years old. It stands 275 feet tall, is 25 feet wide at its base, and weighs approximately 2.7 million pounds.

Ancient Bristlecone Pines

Found high above the normal tree line along the eastern limit of California, the ancient bristlecone pines are recognized as the oldest living individual creatures on Earth. Many of these trees were seedlings when the Egyptian pyramids were constructed and had reached maturity by the time of Christ. The oldest known bristlecone pines are over 4,700 years old. Their wood is extremely dense, and much of the visible structure is dead wood, forming a protective superstructure that supports a thin, living ribbon of tissue within. These resilient trees thrive despite harsh environmental conditions, symbolizing survival and adaptation. Note that regular palm trees are classified as angiosperms, a more recently evolved group of plants. The name "palm trees" can sometimes be confusing due to similarities in appearance but differences in botanical classification with ancient tree ferns.