Dioecy

Fraxinus (/ˈfræksɪnəs/), commonly called ash, is a genus of plants in the olive and lilac family, Oleaceae, and comprises 45–65 species of usually medium-to-large trees, most of which are deciduous (dropping their leaves in autumn), although some subtropical species are evergreen. The genus is widespread throughout much of Europe, Asia, and North America.

The leaves are usually opposite, and mostly pinnately compound (divided into leaflets in a feather-like arrangement). The seeds, known as "keys", are botanically fruits of the type called samara. Some species are dioecious, having male and female flowers on separate plants.

Myriophyllum (water milfoil) is a genus of about 69 species of freshwater aquatic plants, with a cosmopolitan distribution. The centre of diversity for Myriophyllum is Australia with 43 recognized species (37 endemic).

These submersed aquatic plants are perhaps most commonly recognized for having elongate stems with air canals and whorled leaves that are finely, pinnately divided, but there are many exceptions. For example, the North American species M. tenellum has alternately arranged scale-like leaves, while many Australian species have small alternate or opposite leaves that lack dissection. The plants are usually heterophyllous; leaves above the water are often stiffer and smaller than the submerged leaves on the same plant and can lack dissection. Species can be monoecious or dioecious. In monoecious species, plants are hermaphrodite, while in dioecious species, plants are either male or female, the flowers are small, 4(2)-parted and usually borne in emergent leaf axils. The 'female' flowers usually lack petals. The fruit is a schizocarp that splits into four (two) nutlets at maturity.

Schistosoma is a genus of trematodes, commonly known as blood flukes. They are parasitic flatworms responsible for a highly significant group of infections in humans termed schistosomiasis, which is considered by the World Health Organization to be the second-most socioeconomically devastating parasitic disease (after malaria), infecting millions worldwide.

Adult flatworms parasitize blood capillaries of either the mesenteries or plexus of the bladder, depending on the infecting species. They are unique among trematodes and any other flatworms in that they are dioecious with distinct sexual dimorphism between male and female. Thousands of eggs are released and reach either the bladder or the intestine (according to the infecting species), and these are then excreted in urine or feces to fresh water. Larvae must then pass through an intermediate snail host before the next larval stage of the parasite emerges that can infect a new mammalian host by directly penetrating the skin.

Sexual dimorphism is the condition where different sexes of the same species exhibit different morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecious species, which consist of most animals and some plants. Differences may include secondary sex characteristics, size, weight, color, markings, or behavioral or cognitive traits. Male-male reproductive competition has evolved a diverse array of sexually dimorphic traits. Aggressive utility traits such as "battle" teeth and blunt heads reinforced as battering rams are used as weapons in aggressive interactions between rivals. Passive displays such as ornamental feathering or song-calling have also evolved mainly through sexual selection. These differences may be subtle or exaggerated and may be subjected to sexual selection and natural selection. The opposite of dimorphism is monomorphism, when both biological sexes are phenotypically indistinguishable from each other.

Monoecy (/məˈniːsi/; adj. monoecious /məˈniːʃəs/) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system comparable with gynomonoecy, andromonoecy and trimonoecy, and contrasted with dioecy where individual plants produce cones or flowers of only one sex, and with bisexual or hermaphroditic plants in which male and female gametes are produced in the same flower.

Monoecy often co-occurs with anemophily, because it prevents self-pollination of individual flowers and reduces the probability of self-pollination between male and female flowers on the same plant.

Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individuals (dioecy), and their various modes of spatial (herkogamy) and temporal (dichogamy) separation.

SI is best-studied and particularly common in flowering plants, although it is present in other groups, including sea squirts and fungi. In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a matching allele or genotype, the process of pollen germination, pollen-tube growth, ovule fertilization, or embryo development is inhibited, and consequently no seeds are produced. SI is one of the most important means of preventing inbreeding and promoting the generation of new genotypes in plants and it is considered one of the causes of the spread and success of angiosperms on Earth.

Casuarina, also known as she-oak, Australian pine and native pine, is a genus of flowering plants in the family Casuarinaceae, and is native to Australia, the Indian subcontinent, Southeast Asia, islands of the western Pacific Ocean, and eastern Africa.

Plants in the genus Casuarina are monoecious or dioecious trees with green, pendulous, photosynthetic branchlets, the leaves reduced to small scales arranged in whorls around the branchlets, the male and female flowers arranged in separate spikes, the fruit a cone containing grey or yellowish-brown winged seeds.

Ilex (/ˈaɪlɛks/) or holly is a genus of over 570 species of flowering plants in the family Aquifoliaceae, and the only living genus in that family. Ilex has the most species of any woody dioecious angiosperm genus. The species are evergreen or deciduous trees, shrubs, and climbers from tropics to temperate zones worldwide. The type species is Ilex aquifolium, the common European holly used in Christmas decorations and cards.

Ginkgo biloba, commonly known as ginkgo (/ˈɡɪŋkoʊ, ˈɡɪŋkɡoʊ/ GINK-oh, -⁠goh), also known as the maidenhair tree, and often misspelled "gingko" (see Etymology below) is a species of gymnosperm tree native to East Asia. It is the last living species in the order Ginkgoales, which first appeared over 290 million years ago. Fossils similar to the living species, belonging to the genus Ginkgo, extend back to the Middle Jurassic epoch approximately 170 million years ago. The tree was cultivated early in human history, remains commonly planted, and is widely regarded as a living fossil.

G. biloba is a long-lived, disease-resistant, dioecious tree with unique fan-shaped leaves, capable of clonal reproduction, and known for its striking yellow autumn foliage and resilience in disturbed environments. It was known historically as "silver fruit" or "white fruit" in Chinese and called "ginkgo" due to a centuries-old transcription error. It is closely related to cycads and characterized by unique seeds that resemble apricots but are not true fruits.

Self-incompatibility (SI) is a general name for any genetic mechanism that prevents self-fertilization in fertile co-sexual organisms, and thus encourages outcrossing and allogamy. It is contrasted with separation of sexes among individuals (dioecy), and their various modes of spatial (herkogamy) and temporal (dichogamy) separation.

SI is best-studied and particularly common in flowering plants, although it is present in other groups, including sea squirts and fungi. In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a matching allele or genotype, the process of pollen germination, pollen-tube growth, ovule fertilization, or embryo development is inhibited, and consequently no seeds are produced. SI is one of the most important means of preventing inbreeding and promoting the generation of new genotypes in plants and it is considered one of the causes of the spread and success of angiosperms on Earth.

Sexual dimorphism is the condition where different sexes of the same species exhibit different morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecious species, which consist of most animals and some plants. Differences may include secondary sex characteristics, size, weight, color, markings, or behavioral or cognitive traits. Male-male reproductive competition has evolved a diverse array of sexually dimorphic traits. Aggressive utility traits such as "battle" teeth and blunt heads reinforced as battering rams are used as weapons in aggressive interactions between rivals. Passive displays such as ornamental feathering or song-calling have also evolved mainly through sexual selection. These differences may be subtle or exaggerated and may be subjected to sexual selection and natural selection. The opposite of dimorphism is monomorphism, when both biological sexes are phenotypically indistinguishable from each other.

Reversed sexual dimorphism (RSD) is a condition where females of a species are larger or more ornamented than the males. Species prominently displaying RSD include raptors, spiders, the leopard seal, and certain waders; in waders, it is often combined with reversed sexual dichromatism and sex role reversal.

Allocasuarina, commonly known as sheoak or she-oak, is a genus of flowering plants in the family Casuarinaceae and is endemic to Australia. Plants in the genus Allocasuarina are trees or shrubs with soft, pendulous, green branchlets, the leaves reduced to scale-like teeth. Allocasuarinas are either monoecious or dioecious, the flowers never bisexual. Male and female flowers are arranged in spikes, the female spikes developing into cone-like structures enclosing winged seeds.

The genera Allocasuarina and Casuarina are similar, and many formerly in the latter now included in Allocasuarina.