Sex in City Plants, Animals, Fungi, and More. A Guide to Reproductive Diversity.

This book explores how wild plants and animals reproduce in cities. Species that establish durable populations in landscapes of concrete and asphalt constitute a small fraction of the world’s flora and fauna, but their modes of reproduction are nevertheless diverse. Novel sets of reproductive barriers and opportunities in cities have promoted this diversity. How reproductive modes in cities are adapted, or pre-adapted, is a primary focus of this book.

Carolina cranesbill (Geranium carolinianum) has established itself in sidewalk cracks in downtown Philadelphia. Its flowers attract pollinators, but if no pollinator happens to be on hand at the right time, the flowers default within a few hours to self-pollination. This behavior enables Carolina cranesbill in cityscapes to pollinate with or without pollinators.

This Carolina cranesbill flower is about 7 millimeters (¼ inch) in diameter. The flower opens in the morning as functionally female, ready for pollinators. Later in the day it matures as bisexual. If it has not been pollinated, it now self-pollinates. Rebecca Shirk and James Hamrick illuminated pollination in this species.

Here, Carolina cranesbill is rooted in a sidewalk crack. This plant has completed pollination and is setting seed even though its habitat is covered with concrete. Pollinators here are scarce or absent.

The quintessential urban “weed” tree is ailanthus, or tree of heaven (Ailanthus altissima). It illustrates another strategy for propagating in the city. Male and female flowers occur on separate trees. The species depends on insect pollinators for transport of pollen from one tree to another, which may be located blocks away. However, the plant also propagates vegetatively without pollinators, as illustrated below. Compared to a solitary tree, a vegetative colony, or clone, has a potential to produce more flowers and attract more pollinators, theoretically boosting chances of pollination over long distances.

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Sex in City Plants, Animals, Fungi and More is available for purchase from Columbia University Press.

Female tree of heaven in fruit. The fruit consists of yellow samaras produced in clusters scattered about the tree.

Male flowers.

Vegetative propagation of tree of heaven in in a pavement crack between the wall and the sidewalk. Shoots are sprouting from horizontal roots tracking along the crack.

Samaras (elongated membranous structures each bearing a seed).

Female flowers.