Cacti are perennial flowering plants that have adapted to thrive in arid environments. Like all flowering plants (angiosperms), cacti reproduce sexually by producing seeds. These seeds originate within a fruit, which develops after a successful pollination event transforms the cactus flower. Understanding where cactus seeds come from begins with exploring the unique anatomy of the flower that emerges from the plant’s succulent body.
The Reproductive Structure of Cacti
The cactus flower contains both male and female reproductive organs, making the plant generally hermaphroditic. The female structure, the pistil, includes the stigma (a receptive surface for pollen) and the style, which connects to the ovary at the base of the flower. The ovary is the chamber where the unfertilized ovules are housed, waiting to become seeds.
Surrounding the pistil are the stamens, the male organs, consisting of a filament topped by an anther that produces pollen. The flower, along with the spines and new branches, typically emerges from specialized structures called areoles. In most species, the ovary is a single chamber situated below the petals and sepals, giving the flower an inferior position.
From Flower to Seed
The journey from flower to seed begins with pollination: the transfer of pollen from the stamen to the stigma. Cacti rely on various pollinators, including diurnal visitors like bees and hummingbirds, and nocturnal animals such as bats and moths, attracted by the flower’s color, scent, or nectar. Many cacti are self-incompatible, requiring pollen from a genetically distinct plant to produce viable seeds.
Once the pollen grain lands on the stigma, it germinates and grows a pollen tube down the style, delivering male genetic material to the ovule within the ovary. This fusion is fertilization, which initiates the development of the ovule into a seed and the surrounding ovary tissue into the fruit. The fruit protects the developing seeds and serves as the mechanism for their eventual dispersal.
The fruit varies widely across species, ranging from a dry, papery capsule that splits open to a fleshy, often colorful berry. Fleshy fruits include the edible tuna of the prickly pear cactus. Dry fruits may remain on the plant until physically dislodged. Maturation time also varies, with some fruits ripening in weeks and others taking several months.
Natural Seed Dispersal and Longevity
Once the fruit matures, the cactus employs various strategies to disperse the seeds away from the parent plant. Species producing fleshy, sweet fruits, such as the saguaro or prickly pear, rely heavily on animals. Birds, rodents, and other desert fauna consume the fruit, and the hard seeds pass unharmed through their digestive tracts, often being deposited in a new location via scat.
This animal dispersal is advantageous because seeds are often dropped in nutrient-rich microenvironments, such as under a nurse plant or in a sheltered crevice, improving the chance of germination and survival. Cacti with dry fruits, like some barrel cacti, often use wind or water runoff to scatter their seeds after the fruit cracks open. Sometimes, the entire dry fruit attaches to an animal’s fur and is carried a greater distance.
Cactus seeds are adapted for longevity, allowing them to survive the unpredictable desert conditions. They often enter dormancy, forming a persistent soil seed bank that can remain viable for many years. Germination is frequently triggered by specific environmental cues, such as heavy or prolonged rainfall, which signals sufficient conditions for a seedling to establish itself.
Harvesting Cactus Seeds for Cultivation
Human cultivation involves collecting seeds at the point of fruit maturity. Growers must monitor the fruit for signs of ripeness, which typically include a change in color (such as green to red or yellow) or the fruit drying out and splitting open. Harvesting too early results in non-viable, underdeveloped seeds.
Extracting seeds from fleshy fruit requires separating them from the sticky pulp, which can inhibit germination and encourage fungal growth. This is often achieved by mashing the fruit in water, allowing the pulp to float and the heavier seeds to sink, before straining and thoroughly rinsing. Seeds from dry pods, like those from Mammillaria species, are simpler to process, often requiring only that the pod be gently crushed or shaken to release the contents.
After cleaning, the seeds must be completely air-dried in a warm, shaded area for several days to prevent mold and preserve viability. Once dried, they are stored in a cool, dark, and dry container, such as a paper envelope or a sealed glass vial, until they are ready to be sown for propagation.