(Photograph = Mammillaria pectinifera, Lourdes)
Introduction
Serotiny is delayed seed dispersal: mature seeds are held on the parent plant and released later, often when conditions improve. In arid habitats, that delay can spread risk across seasons and help seedlings catch rare wet pulses.
The details
Mammillaria pectinifera is a small, globose cactus endemic to the Tehuacán Valley of Puebla, Mexico. Plants are about 3–4 cm in diameter with white, comb-like spines that shade the stem. Flowers form a crown near the apex. Fruits are pale, embedded berries that may remain in the stem for years, releasing seeds gradually through a tiny apical opening—or be expelled whole in the year they mature.
In dry years, fruits are mostly retained, and seeds trickle out over time from those retained fruits. In a wet year, a noticeable share of new fruits is expelled from the plant, dumping many more seeds at once when conditions favor establishment. In the field, no fruit expulsion was seen in a dry year, while in a wetter year about one-fifth of new fruits were expelled, and seedling establishment was roughly five times higher. Under greenhouse watering, very high moisture drove near-complete expulsion of fruits.
Retained fruits act as a seed bank on the plant. During the first year after fruiting, roughly two-fifths of the seeds can remain inside a retained fruit; those seeds are released gradually as the fruit ages, and seeds in retained fruits remained viable as they aged. Expelled fruits, by contrast, come from the newest cohort and release their entire seed load quickly.
Bottom line. The species uses two strategies tied to moisture. In average or dry conditions, slow, background release hedges bets. During unusually wet periods, rapid release from expelled fruits floods the ground with seeds when seedlings are most likely to survive.
Additional Reading: Seed Retention and Release in Mammillaria pectinifera
