Why are the seed cones of conifers so diverse at pollination?

When we think of pollination we think of flowers or blossoms, but this is only part of the story. Many plants pollinate without flowers, such as conifers. They produce male and female cones. Pollen blows from the male cones to land in the female cones. That takes a lot of pollen, and explains why the hayfever season starts with tree pollen for many people.

The problem for female cones is the same for any conifer, how to catch pollen on the breeze. It’s the same problem for all gymnosperms, yet they have various solutions. You can recognise what cones belong to what species.

Losada and Leslie use conifer species in the fir (Abies) and spruce (Picea) lineages of the pine family (Pinaceae) to investigate the evolutionary mechanisms leading to reproductive diversity among wind-pollinated plants. Abies and Picea are thought to draw in pollen in slightly different ways. Abies may use rainwater to move pollen into its ovules following pollination while Picea ovules exude an aqueous pollination drop to move the pollen.

The authors used Abies koreana and Picea jezoensis cones from trees growing in the Arnold Arboretum of Harvard University. They tested whether cone morphology influences pollination function through natural and artificial pollination experiments. For natural pollination, they sampled cones every other day during the pollination period, dissected them, and recorded the position of pollen grains. For artificial pollination experiments, they first collected cones that had opened but had not yet received pollen and then artificially pollinated them in a wind tunnel.

Wind tunnel analyses using these cones suggest that different morphologies are equally effective in capturing pollen, demonstrating how simple differences in development can give rise to equally functional morphologies. Losada and Leslie conclude: “In the absence of clear functional differences among cones, neutral variation in cone scale development appears to be the primary reason for diverse pollination-stage morphologies exhibited by Pinaceae.”