A practical field guide to New Zealand's native edible plants. Andrew Crowe
Gardener's Encyclopaedia of NZ Native Plants by Cave, Paddison
Trees and Shrubs of New Zealand by Poole and Adams
The Reed Field Guide to New Zealand Native Trees by J.T. Salmon
High Altitude Mountain Daisies (Celmisia Semicordata), Mt Cook NP, Canterbury, New Zealand
18 in. x 24 in.
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Monoecious and dioecious plants.
Coprosma lucida female
Coprosma lucida male
One of the intriguing features of the New Zealand flora is the high percentage of plants that have separate male and female individuals. While this is the norm in animals, plants that have male and female sex organs on different individuals is unusual.
Male flowers are those whose gametes (pollen) leave the flower, while female flowers are those whose gametes (ova) remain in the flower and are receptive to the male gamete.
Monoecious plants have the 2 sexes on the same plant, with all individuals producing male pollen and female eggs and seed. Monoeciousness is the norm in most plants of the world.
Some monoecious plants can be classed as hermaphrodite with flowers which contain both male and female parts.
In many hermaphrodite flowers there is a time when the flower is male with anthers distributing pollen, and a time when they are female, with a receptive stigma. By timing their sex expression the plant increases the likelihood of being pollinated by another member of the same species. The pollen would not be shed when the ovary was ripe. Usually the female stigma is receptive after the pollen is shed. Outcropping or fertilization by another member of the same species is encouraged, which enhances variety within the species
Monoecious plants have separate male and female flowers found on the same plant. The same idea of timing the male and female functions to maximize the chance of cross pollination occurs but the likelihood of self pollination is increased.
Dioecious plants have male and female flowers on separate plants. Exotic plants that this occurs in include Kiwi fruit and Cannabis sativa which have male and female plants. A characteristic of the The New Zealand flora is the high % of plants that have the sexes on separate plants (dioecious). Approx 12-13% of our flora are dioecious. (Britain 2-5%, South Australia, 3.9%., Hawaii 5%). However in any plant association there may be up to 50% of the individuals who exhibit dioeciousness
The significance of dioeciousness to the propagator of seeds is that female plants need to be sourced if seed is to be collected.
Dioeciousness of plants account for the variability in seeding from year to year that some species exhibit because seeding will be determined by synchronising the time at which the male and female parts are functional. Rimu may go 7-12 years before seed on females is produced in abundance. These years are termed mast years.
As a male tree may be some distance from a female tree, the environmental conditions that determine flowering would be more variable in separate trees than the same tree. There is more likelihood of reproductive failure if the nearest tree of the opposite sex is some distance away. The fact that pollen from a distant tree must fertilise a female tree may put the successful reproduction and production of viable seed under stress. Logging of a population, and a reduction in total density of the adult trees and total gamete production will reduce the likelihood of fertilisation . This seems to be the case in Monoao( Dacrydium kirkii), a dioecious species of conifer that grows in Northlands kauiri forests.Monoao has become relatively rare in the wild with its natural range vastly reduced to remnant populations in Coromandel, Northland and Little Barrier Island.
The ratio between the number of plants of a species that are male or female will influence the availability of seed of the dioecious species.
If a plant is grown for the beauty of its seeds (Porokaiwhiri) or flowers (Clematis) growing from seed will produce some individuals who are not of the desired sex. In these cases reproduction by cutting is suggested.
A significant excess of males or females may exist in natural populations. Usually Coprosma have more males than females in their populations.
A feature related to separate male and female trees is Sexual dimorphism. This is that male plants have different form or shape than females. Of course in most animals this is obvious with the male having a different body shape to females. In plants however it is less obvious but does exist. Male Coprosma show broader leaves to female Coprosma.
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