Phylloglossum

What is Phylloglossum?

Phylloglossum is a plant genus within the order Lycopodiales, commonly known as club mosses. It consists of a single species, P. drummondii, which is native to Australia and New Zealand.¹

Standing only 3 to 5 cm (1 to 2 inches) tall, this unique plant features a bulblike underground base and a small cluster of succulent, spike-shaped leaves. It also produces a single stalk topped with a cluster of scalelike leaves that bear sporangia. A notable aspect of its life cycle is its adaptation to seasonal changes: the plant dies back to a tuber during the dry season and emerges again when the rains return.¹

What are club mosses?

Club mosses are a group of approximately 400 species of seedless vascular plants that make up the family Lycopodiaceae, the only family within the lycophyte order Lycopodiales. Despite their name, they are not true mosses, which are nonvascular plants; instead, club mosses are considered “fern allies”.²³

These plants are typically low-growing, evergreen herbs characterized by needlelike or scalelike leaves. Many species produce conelike clusters of small leaves known as strobili, which house spore-producing capsules. They are homosporous, meaning they produce only one type of spore, and they exhibit an alternation of generations between a spore-producing sporophyte and a sexual gametophyte.²⁴

While modern club mosses are small and herbaceous, they are the survivors of a diverse and ancient group of plants that were prominent in the massive coal-forming swamp forests of the Carboniferous Period. Today, they are found primarily in tropical mountains and northern forests across both hemispheres.⁵²

How do plants survive in dry climates?

Plants that thrive in dry climates, known as xerophytes, have evolved various morphological and physiological mechanisms to survive water scarcity by minimizing water loss and maximizing storage.⁶⁷

Water Storage and Conservation

Many xerophytes are succulents, which possess thick, fleshy tissues in their stems or leaves designed to store water. To prevent transpiration—the loss of water through leaf pores called stomata—these plants employ several strategies:⁸

• Physical Barriers: They often feature waxy cuticles, dense hairy coverings (trichomes), or sunken stomata to protect against evaporation.⁶⁹
• Leaf Modification: Many desert plants have minute leaves or lack them entirely, such as cacti, while others may shed their leaves during drought periods to eliminate water loss.⁶⁹⁷
• Photosynthetic Adaptations: Many succulents use crassulacean acid metabolism (CAM). This allows them to keep their stomata closed during the hot, dry day and open them only at night to take in carbon dioxide, significantly reducing water loss.⁸⁹¹⁰

What is the role of sporangia in plant reproduction?

The sporangium serves as the essential spore-producing structure in the life cycle of plants, acting as the site where meiosis occurs to generate reproductive spores. Within these structures, specialized cells known as sporocytes (or spore mother cells) undergo division to form spores, which eventually develop into the gametophytic phase of the plant.¹²¹³

The role and complexity of sporangia vary across plant groups:

• Spore Production: In vascular plants, sporangia house the developing spores, often surrounded by nutritive tissue. In homosporous plants, a single type of sporangium produces one type of spore, while in heterosporous plants (including all seed plants), distinct microsporangia and megasporangia produce male and female spores, respectively.¹³¹²
• Dispersal Mechanisms: Sporangia have evolved various methods to release spores. For example, many ferns utilize specialized cells called annuli that create mechanical stress as they dry, eventually snapping open to launch spores into the air.¹⁴¹⁵
• Structural Organization: Sporangia are often grouped into clusters called sori, which may be protected by specialized structures like the indusium, or borne on specialized leaves or cones known as strobili.¹⁴¹²¹⁵