Trees with long seed pods are a common sight. These distinctive pods protect developing seeds and play a significant role in how new trees establish themselves. Understanding these pods can reveal much about the trees that bear them.
Trees Known for Long Seed Pods
The Northern Catalpa (Catalpa speciosa) produces slender, bean-like pods that can reach lengths of 10 to 24 inches. These pods are green in summer, turning dark brown and splitting lengthwise in the fall to release winged seeds. Catalpa trees also feature large, heart-shaped leaves and showy white flowers that bloom in late spring.
The Honey Locust (Gleditsia triacanthos) is another common tree with long pods. Its pods are flattened, leathery, and often twisted, varying in color from green to dark purple-brown or black, and can grow 6 to 18 inches long. Unlike catalpa, honey locust pods typically persist on the tree through winter and often require animal consumption for seed release. This tree is also identifiable by its compound leaves with many small oval leaflets and, in many varieties, sharp thorns on the trunk and branches.
The Black Locust (Robinia pseudoacacia), a relative of the Honey Locust, also produces seed pods. These smooth, flat pods are typically 2 to 4 inches long, dark brown or black, and contain four to eight seeds. Black Locust trees have fragrant white flowers that bloom in late spring and compound leaves, often with a pair of short thorns at the base of each leaf.
The Kentucky Coffeetree (Gymnocladus dioicus) is notable for its robust, thick-walled, reddish-brown to purplish-brown pods, 4 to 10 inches long and 1.5 to 3 inches wide. These pods are filled with a sticky pulp surrounding hard, dark brown seeds. The Kentucky Coffeetree is recognized by its very large, twice-compound leaves and its coarse, scaly bark. Its pods often remain on the tree through winter, contributing to its distinctive appearance.
Understanding Long Seed Pods
Botanically, a “pod” is a type of fruit, specifically a dry fruit that develops from a flower’s ovary and typically splits open to release its seeds when mature. This protective structure encloses the seeds. The development of a seed pod begins after a flower is pollinated and fertilization occurs, leading to the growth of ovules into seeds within the ovary. As the seeds mature, the ovary expands and transforms into the fruit or pod.
Long seed pods can be categorized into different botanical types. Legumes, characteristic of the pea family (Fabaceae) to which locusts and coffeetrees belong, are typically dry fruits derived from a single carpel that split along two seams to release seeds. Capsules, such as those found on catalpa trees, are dry fruits that originate from a compound ovary and split open in various ways. These structures serve the fundamental purpose of safeguarding the developing seeds until they are ready for dispersal.
The Journey of Seeds: Pods and Dispersal
Long seed pods play a significant role in the dispersal of seeds, which is the movement of seeds away from the parent plant. This process is important for plant survival, helping to reduce competition for resources between parent and offspring and enabling plants to colonize new areas. Various mechanisms facilitate seed dispersal, and the characteristics of the pod often determine the primary method.
Wind dispersal, or anemochory, is a common method for trees with long pods. Seeds within pods, especially those that are lightweight or possess winged structures, can be carried by air currents over considerable distances. For example, the flat, winged seeds released from catalpa pods are well-suited for wind transport once the pods split open.
Gravity dispersal, or barochory, occurs when heavy pods or seeds simply fall from the tree. The substantial pods of the Kentucky Coffeetree, for instance, typically drop directly to the ground. Once on the ground, these seeds may then be further dispersed by animals or water. Animal dispersal, or zoochory, is also crucial, especially for pods like those of the Honey Locust and Kentucky Coffeetree, which contain a sweet pulp that attracts wildlife. Animals consume the pods, and the seeds, often protected by a hard coat, are later deposited in new locations.