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division to produce haploid microspores. Biennials are also herbs, but, unlike annuals, their growing cycle spans two years: the vegetative (nonreproductive) plant growth takes place from seed during the first year, and flowers and fruit develop during the second. Although they were superficially similar in habit to the cycads, with a squat trunk and often pinnately divided leaves, their reproductive structures were different, and their actual relationship is not close. Water is generally required for them to swim to the eggs for fertilization. Pteridosperm seeds were very similar to those of cycads and were often large, with a soft outer seed coat and a harder inner seed coat.
During the course of the evolution of the seed habit, a number of morphological modifications were necessary. Woody forms (generally trees and shrubs ) are rich in secondary tissues, while herbaceous forms (herbs) rarely have any. Many cycad species host cyanobacteria (also known as blue-green algae) in nodules in the roots and may form coralline masses on the ground surface known as coralloid roots. Some lateral roots of mangroves become specialized as pneumatophores in saline mud flats; pneumatophores are lateral roots that grow upward (negative geotropism) for varying distances and function as the site of oxygen intake for the submerged primary root system. Coexisting with the cycads during the Mesozoic was another group of gymnosperms, the cycadeoids (division Cycadeoidophyta ). Family (to work out which Genera belong to each).