The primary plant structure includes plant leaves, but some exceptions lack this classic plant structure. The world is an incredible place with different plants separated from each other using different identifiable traits. 

One of the ways to distinguish plants is whether or not they have vascular tissue or seeds. Humans identify and have grouped plants in 12 species according to their characteristics. Most plants have leaves, but some plant species don’t have leaves and thus conduct photosynthesis through their stems; others lack stems.

Understanding Plants Without Leaves

When you think of a plant, most people imagine something green or green leaves, a stem, branches, and flowers, which is a description fit for vascular plants. However, there are other plants called non-vascular plants, which don’t have the basic vascular system. Examples of such plants are bryophytes and plants like liverworts, mosses, and hornworts, much smaller than vascular plants. They have flat, green bodies and short central stems with small structures resembling a leaf.

The assumption that all plants have leaves is not correct, especially considering that some microscopic algae and some parasitic plants have none. There are other plans whose leaf-structures have been reduced to very small scales, making them appear leafless such as the Garden Asparagus with triangular scales.

Plants are classified into Non-vascular and vascular plants, and the different classification groups differ in structure, habitat, and size. Non-vascular plants such as hornworts, mosses, liverworts, and a few algae exceptions are small in size. They lack the functionality that other plants do, such as a transportation system to exchange water and gases. These plants use spores for reproduction instead of seeds, and they have specialized tissues for the transportation of minerals and water.

Bryophytes

There are many examples of this basic plant structure, such as Bryophytes, which are plants without leaves. Such plants usually have thalloid bodies meaning that they don’t have differentiated stems, leaves, or roots. 

The gametophyte stage subjugates the life cycles of these plants. All the vegetative parts of Bryophytes belong to the most dominant and familiar form where a sporophyte appears for a limited period. This is inclusive of the photosynthetic leaf-like structures, the stem, thallus, and rhizoids anchoring the plant to its substrate.

They have unbranched sporophytes and lack an actual vascular tissue with lignin. However, some have specialized tissues to facilitate the transportation of water through the leaf.  Bryophytes lack roots or stem to aid in the movement of water and minerals, which is why they grow only in moist places to prevent drying out. 

These plants are non-vascular, meaning that they don’t have tracheids, and instead, water is transported through some special conducting cells. Bryophytes don’t have leaves, leaves, or stems, but they are green plants such as Anthoceros, Marchantia, Funnaria, Riccia. They are divided into three species, liverworts, mosses, and hornworts.

Anthoceros

Anthoceros is a Bryophyte belonging to the hornworts genus and the Anthocerotaceae family. These plants produce a characteristic horn-shaped sporophyte, hence their name meaning, “flower horn.” This classification includes about 200 plant species in the world, and although Anthoceros plants are cosmopolitan, they mostly grow in tropical and temperate climates. These plant species are found in shady places such as rocks and ditches and moist areas.

Hornworts

Hornworts are examples of Anthoceros plants that lack a vascular system, and they don’t have leaves.

As the name suggests, hornworts have a thorny structure, with most species forming minor and small blue-green marks. Hornworts were traditionally grouped as Bryophytes, but they are classified under horned liverworts in some classification systems.

However, there is evidence that hornworts have a molecular differentiation from liverworts and mosses, and there is a distinct evolutionary history that places the plants in their specific taxonomic divisions.

Funaria

Funaria refers to a classification of plants such as moss, which grow in dense areas or moist shady, calm, and rainy places. These plants have a height of between 3-5 cm, and they have a radial symmetry with multicellular branched and colorless rhizoids for phylloid, leaves, or stem axis differentiation.

Moss

Moss is an example of a bryophyte, non-vascular, non-flowering, and one of Earth’s earliest land plants found mostly in terrestrial and wet areas. Moss lacks the basic vascular system, so they don’t have stems, roots, or leaves. It is a non-vascular plant, meaning that it doesn’t have an internal system for water transportation, which affects its growth. This plant spreads out to cover the ground as it grows to less than 9 inches tall.

Mosses don’t have real leaves; instead, they have Microphylls, which are leaf-like structures found on the stem. 

These structures have one unbranched vein, which develops from small bits of tissue. Mosses are green plants, almost similar to algae but with a slightly different stem and leaf-like structure. Mosses can manufacture their own food, even without leaves, because they contain chlorophyll, and they can be found on branches, tree trunks, soils, rocks, and in water.

Marchantia

Marchantia refers to a genus classification of plants in the Marchantiaceae family. They are a group of liverworts that display distinction in a lower storage layer and an upper layer for photosynthesis that has an epidermis with pores.

Liverworts

Liverworts are plants without leaves that are mostly found in tropical climates. They are classified as either leafy or branching, leafy referring to those found on trunks of trees in wet woods, and branching referring to thalloid liverworts, which help in the disintegration of rocks, decaying of logs, and provision of food for animals. Their thalloid liverworts do not have any resemblance to mosses. They don’t have leaves or stem structures but just the main body instead.

Liverworts are often found growing with mosses, and they do not develop seeds and flowers. The leafy liverworts have stems with leaves grouped into two or more rows and can be easily mistaken for mosses. The thalloid liverworts, on the contrary, have a thallus structure that is fleshy and thick. 

An example of a liverwort without leaves is the Riccia fluitans, which is one of the three evolutional, non-vascular plants. They do not have cells for water conduction, and they reproduce through haploid photosynthesis through an alternation of generations. These plants are very small and thalloid, and they don’t have the primary root, leaf, and stem differentiation of vascular plants.

Liverworts have a single cell layer, and they lack stomata, which permits photosynthetic processes in advanced plants. They also have rhizoids in place of the roots for anchorage and absorption of water. Liverworts were initially classified as Bryophytes with mosses and hornworts, but further research brought about other classifications.

Angiosperms

Some Angiosperms don’t have leaves, and the most popular is the cactus. A cactus is a flowering plant that does have leaves. This plant is usually found in arid and dry climates which not have a lot of water.

Cactus

Angiosperms such as cacti have succulent stems for storage of water for a long. Cacti lack leaf structures, but they have external appendages such as thorns for protection against predators. A cactus plant grows in xeric conditions, which means that it needs water storage, which is achieved through the thorns or the spine from modified leaves. 

The thorns of cacti plants don’t have the morphological ability to carry out photosynthesis because they long lost their function as leaves but instead function as protection from herbivores and other predators. They act as distinct parts or remnants of what was once was leaves, which have evolved to form a different atomically part of the plant functionally.

Cacti plants have slender, conical parts that cover the young pad, and as the pod matures, the leaves fall off and are replaced by spines. A cactus’ main body is made of modified stem material rather than leaves, just like most desert plants, which bear leaves in rainy seasons and shed the leaves off when it dries up, which is most of the time. The spines of cactus plants can’t perform photosynthesis. Thus cacti depend on a succulent-specific process known as CAM photosynthesis for the function.

Other plants without leaves

Lichens

Lichens are non-vascular plants, but not all types are considered truly plants as they lack stems, roots, and leaves. Lichens have fungus and an alga component, which both live in a relationship with one another, forming a single plant. They can be found on soils, trunks, rocks, and tree branches, but rarely in water.

Algae

Algae are considered the simplest of green plants, and they are found in a lot of places with sufficient moisture, such as on twigs, rocks, soils, tree trunks, shrubs, and in fresh and salty waters.

Leaves are crucial for most plants’ survival, but they are not found on all plants growing on the surface of the Earth. As such, plants that lose leaves due to shedding can also survive, especially if the roots and stems are still thriving. Most plants have leaves, even if the leaves look like glass blades. However, such plants as mushrooms, lichens, and some fungi lack leaves. Some types of algae, such as seaweed, lack leaves, flowers, and roots as well, so they cling to shells, stones, and rocks underground.