Are All Plants Limited To Secondary Growth?

Meristems play a crucial role in both primary (taller/longer) and secondary (wider) growth in plants. Primary growth is controlled by root apical meristems or shoot apical meristems, while secondary growth is controlled by the two lateral meristems, the vascular cambium and the cork cambium. Not all plants exhibit secondary growth, as animals exhibit determinant growth, which grows to a specific body size and shape before stopping growth.

Plants with secondary growth also grow in diameter, especially for plants that grow for several growing seasons (perennial). These plants produce an additional lateral meristem called the cork cambium, which produces cells that form a new skin called the periderm. Unlike the vascular cambium, the cork cambium usually is not.

Secondary growth is often used synonymously with tissue expansion at the organ or plant scale and over short time periods, while over longer time periods, the increase in biomass is a common metric. Secondary growth occurs in most seed plants, but monocots usually lack it. Annual plants do not have secondary growth, while perennials (e.g., trees) have secondary growth.

Secondary growth, or “wood”, is noticeable in woody plants, but occurs very rarely in monocots. It is a characteristic feature of dicotyledons, with every year cambium forming secondary xylem on the inner side and secondary phloem on the outside. Today, secondary growth occurs only in seeds plants, but it was recorded in fossils of progymnosperm, an extinct clade of spore-bearing plants. Herbaceous plants, like monocots and herbaceous eudicots, only grow for one growing season (annuals) and do not present secondary growth.

Do bryophytes have secondary growth?

Bryophytes are capable of undergoing secondary growth.

Can a plant have both primary and secondary growth?

Woody plants undergo primary and secondary growth simultaneously, with primary growth occurring in root tips and shoot tips, and secondary growth in older regions like stems and roots. Growth in plants involves increased stem length and girth, elongated roots, and stem lengthening in meristematic zones. Growth occurs in all four stages: seeding, sprouting, newly produced plant, and old plant. Hormones synthesized by plants also influence growth. Primary growth, primarily in shoot and root tips, is facilitated by apical and intercalary meristems, which aid in plant elongation and development.

Do any monocots have secondary growth?

Monocots typically do not undergo secondary growth. Even when they increase in girth, as is the case with palm trees and yucca plants, this does not result in the development of a secondary xylem and phloem. This phenomenon is known as anomalous thickening.

Do dicots have secondary growth?

Secondary growth in dicots occurs when stems and roots grow wider, often resulting in the development of a woody stem. This stem is formed through the activities of the stem’s vascular cambium and cork meristem tissues. However, not all dicots undergo secondary growth, such as tomato, carrot, and potato plants. Monocots, like palm trees and yucca plants, do not undergo secondary growth, and an increase in girth without secondary growth is called anomalous thickening.

Do all dicots have secondary growth?

Abnormal secondary growth in plants does not follow the pattern of a single vascular cambium producing xylem to the inside and phloem to the outside as in ancestral lignophytes. Some dicots have anomalous secondary growth, such as in Bougainvillea, where a series of cambia arise outside the oldest phloem.

Ancestral monocots lost their secondary growth and their stele changed in a way that could not be recovered without major changes. Monocots either have no secondary growth, have an “anomalous secondary growth” of some type, or enlarge their diameter in what is called a sort of secondary growth or not depending on the definition given to the term. Palm trees increase their trunk diameter due to division and enlargement of parenchyma cells, which is termed “primary gigantism” because there is no production of secondary xylem and phloem tissues.

In some other monocot stems, such as Yucca and Dracaena with anomalous secondary growth, a cambium forms but produces vascular bundles and parenchyma internally and just parenchyma externally. Some monocot stems increase in diameter due to the activity of a primary thickening meristem, which is derived from the apical meristem.

In summary, abnormal secondary growth in plants does not follow the pattern of a single vascular cambium producing xylem to the inside and phloem to the outside, as seen in ancestral lignophytes.

Which plants have no secondary growth?

Primary growth is the primary process in all plants, but most dicotyledonous plants also exhibit secondary growth. This is not typically observed in monocots due to the absence of vascular cambium. The lateral meristems involved in secondary growth include intrafascicular cambium, interfascicular cambium, and cork cambium.

Conifers, grasses, and cyclads are examples of gymnosperms that do not exhibit secondary growth due to their lack of vascular cambium. Deciduous angiosperms, which include secondary xylem, phloem, medullary rays, cork, and cortex, are the primary tissues in dicotyledons.

As a tree grows, the majority of its secondary xylem or wood turns dark brown, particularly in the older parts of the stem. This is due to the progressive filling and deposition of organic compounds in the vessels and tracheids of older secondary xylem. Therefore, secondary growth occurs in angiosperms.

Do tomatoes have secondary growth?

Secondary growth is evident in tomato stems near the base of the stem.

Do gymnosperms have secondary growth?

The gymnosperm stem exhibits complete secondary growth due to vascular tissue growth and a well-developed periderm. The cortical parenchyma is below the periderm, with loose cell organization and intercellular spaces. The stem is diverse, containing structural proteins, carbohydrates, glycoproteins, types, lipids, proteins, carbohydrates, and more. It also demonstrates permeability, fluidity, asymmetry, repairing, synthesis, transport, adhesion, and cell junctions.

What plants only have primary growth?

The shoot of a plant grows in length and thickness, giving rise to lateral organs such as branches, leaves, flowers, fruits, and seeds. Primary growth stems increase in length and thickness based on the apical shoot meristem and intercalary meristem activities, while secondary growth stems increase in diameter through the activity of the vascular cambium and cork cambium.

Primary growth occurs when the apical shoot meristem is restricted to the stem’s tip, and growth occurs by increasing cell size. However, palms and other monocots may have very thick stems by adding new vascular bundles and increasing the number of parenchyma cells, referred to as anomalous growth. This growth is a consequence of the secondary growth meristem, which is more superficial than the vascular bundles and gives parenchyma cells outward and parenchyma cells and vascular bundles inward.

Apical caulinar meristems release inhibitory substances, including hormones, carbohydrates, and other signaling molecules, which are released by the apical caulinar meristem. As the stem elongates, the older axillary buds get far from the apical caulinar meristem influence, leading to their activation.

In summary, all plant species perform primary growth, with palms and other monocots showing anomalous growth due to the secondary growth meristem.

What plants have secondary growth?

Woody plants, including trees, shrubs, and vines, undergo secondary growth, which is the outward expansion of the plant. This results in thicker and wider plant growth, which is essential for their taller growth and increased stem and root support.