SEX - INFO

sex

dioecious
sex

monoecious
sex

bisexual
sex

male
sex

female
sex

heterostylous

  SEX 

 MALE

The flowers are male, having stamens but no carpels.


 FEMALE

The flowers are female, having carpels but no stamens.


 BISEXUAL

Every flower on the plant has both male (stamens) and female (carpels) structures. Alternative names for bisexual are: androgynous, hermaphroditic, monoclinous and synoecious. Recent studies in the likely most recent ancestral flower of angiosperms suggests that the most recent ancestral flower was bisexual, and that unisexual flowers evolved independently many times afterwards. (The ancestral flower itself is at the moment as elusive as ever).


 OR  UNISEXUAL

The plant can be either Monoecious or Dioecious, see below.


 MONOECIOUS

Many plants are Monoecious, that is have separate male and female flowers where both occur on the same plant. Monoecious plants can pollinate each other and (probably) themselves too.


 DIOECIOUS

Much fewer plants are Dioecious where separate male and female flowers are on separate plants.

This has reproduction implications: both male and female plants need to be nearby in order for fertilization of female flowers by male flowers to occur. If fertilization does not occur, a female plant will not produce fruit or berries (but a male plant will always produce pollen). In dioecious plants it is generally that the male flowers last much longer than the female flowers which turn to fruit soon after being fertilised. The male flowers just keep on going ready to fertilise other female plants of the species.


 &  &  POLYGAMOUS

Alternative names for polygamous are androgynomonoecious, polygamomonoecious and trimonoecious.
Having both bisexual & (male &/OR female) flowers on the same plant. i.e. bearing both unisexual and hermaphrodite flowers on the same plant.


 OR  OR  POLYGAMODIOECIIUS

Having either bisexual OR male OR female flowers on separate plants.


 EOR  GYNODIOECIOUS

Having a mixture of bisexual/hermaphrodite flowers on some plants and only female flowers on other plants. These might include male plants, sterile plants (male sterile or female sterile) and hermaphrodite plants - and a little-known fourth class of partially male sterile plants where temperature influences sexual expression and the degree of male sterility but not in the former 3 classes. Examples of gynodioecious flowers include Buck's-horn Plantain, Bladder Campion, Devil's-bit Scabious and Meadow Saxifrage


 EOR  ANDRODIOECIOUS

Having bisexual and male flowers on separate plants.


 &  ANDROMONOECIOUS

Having both bisexual and male flowers on the same plant. examples include Hellebores such as Stinking Hellebore.


 &  GYNOMONOECIOUS

Having both bisexual/hermaphrodite and female flowers on the same plant. Examples include Catchfly and many plants belonging to the Asteraceae family (Dandelion & Daisy).


 HETEROSTYLOUS 


pin


thrum

Heterostylous - having two forms of bisexual flower: Pin and Thrum, either of which can only fertilise the opposite form. Pin forms have a long style and short stamens, whereas thrum forms have long stamens and a short style. Because the pin and thrum forms are determined by genes, the same plant has either all pin flowers or all thrum flowers (the Author thinks). See Primrose for a much fuller explanation and for information on further forms.

Purple Loosestrife takes heterostyly to the third level where there are three types of flower morphs. It is thus Tristylous. Each flower morph has two types of stamens (but only one stigma). The two types of stamens are in sets of (nominally) six each. The first morphological type where the style is short and the two stamens are medium and long; the second morph has a medium length style and long and short stamens; the third morph has a long style with medium and short stamens. Pollen transferred from flowers of the same morph will not result in fertilization because the individual morphs are self-incompatible. The three flower morphs are adapted to pollination by different insects. Generally, pollen from the stamen nearest to the stigma will pollinate the stigma.


Protandry
A protandrous flower is one in which the stamens shed pollen before the stigma is receptive. Examples being the flowers of Jacob's Ladder (Polemonium caeruleum) and Foxglove (Digitalis purpurea). A protandrous flower is first functionally male and afterwards functionally female, but not both at the same time. This is only one of the ways in which some plants try to protect themselves from self-fertilisation.

But in the case of Foxglove (Digitalis purpurea), where the flowers open from the bottom upwards in the long spike and there is a time when the fully opened females at the bottom are concurent with the freshly-opening males nearer the top. Pollinators often start from the bottom with the female flowers then work their way up to the males nearer the top, thus they have not pollinated any flowers on the plant. But when they move on to the next Foxglove plant they pollinate the female flowers at the bottom with pollen from a differing Foxglove, thus helping cross-pollination and hindering self-pollination.


Protogyny
A protogynous flower is the opposite of a protandrous flower. The stigma is receptive to pollen before the anthers open and release their pollen, during the interval the stigma becomes unresponsive to pollen. Thus self-fertilisation is again thwarted. Examples of flowers exhibiting protogyny include the flowers of Common Figwort (Scrophularia nodosa), Greater Plantain (Plantago major), Christmas-Rose (Helleborus niger), Horse-Chestnut (Aesculus hippocastanum), Magnolia, Hortonia and Daphnandra. Other good examples are Meadow Crane's-bill (Geranium pratense), Red Campion (Silene dioica), Honeysuckle (Lonicera periclymenum) and Pink (Dianthus plumarius). There are many more, including Grass-of-Parnassus (Parnassia palustris) where the stamens take up a definite position in space as time progresses.

In Greater Plantain (Plantago major) the (female) stigmas are exposed first starting at the bottom and the stamens only start appearing after the stigmas have withered. Thus stamens are at the bottom and stigmas above them further up the long this inflorescence. This strategy largely prevents self-pollination.

Lords and Ladies (Arum maculatum) is also protogynous but with a slightly different strategy. At first both male and female flowers deep within it are sterile. But then one day the female sexual organs deep within the spadix become active and they release an odour attracting the tiny Diptera flies which then become trapped by the expanding but still sterile male flowers in a ring above the female flowers at the bottom. On the second day the male flowers become active and allow the trapped flies to escape, and as they do so they unintentionally take sticky pollen grains with them. When they visit another Lords-and-Ladies flower they fertilise it with the pollen.


Dichogamy / Dichogamous
Both Protogyny and Protandra are examples of Dichogamy where the stamens and stigmas of bisexual flowers ripen at differing times in order to prevent self-fertilisation.


Homogamy / Homogamous
Definition a) : Homogamy is the antonym of dichogamy and is where both male and female organs of the plant mature at the same time. Therefore it is capable of self-fertilisation - providing all other factors are favourable.
Definition b) : in the case of the Asteraceae family Homogamous heads consist of just one type of floret - either all ray florets (as in Dandelion (Taraxacum officinale) or all disc florets (as in Pineappleweed (Matricaria discoidea) or Tansy (Tanacetum vulgare).


Heterogamy / Heterogamous
Heterogamous flowerheads are where the heads comprise two differing sexes of florets, examples being the ray (which are either unisexual or neuter) and disc florets (which are usually usually bisexual) belonging to the Asteraceae (Dandelion & Daisy family). Alternatively, it can mean bearing two (or more) sorts of flowers in one cluster of flowers.


Plant sexuality is not always so straightforward, there are many half-way houses and permutations on the above.  Plant Reproductive Morphology

NOTES ON BOOLEAN EXPRESSIONS:

  • 'EOR' or '⊕' is the Logical 'Exclusive OR' (sometimes spelled 'EXOR' or 'XOR') being 'either one or the other', but not both.
  • '&' is the Logical 'AND' meaning both at the same time.



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