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Orchids, Anatomy of orchids: stem, flower, leaves, roots

Orchids, Anatomy of orchids: stem, flower, leaves, roots


OUR ORCHIDS FRIENDS

ANATOMY OF ORCHIDS

FLOWER

The amazing orchid flower consists of six tepals (in plants where there is no distinction between calyx and corolla, the elements that make up the flower are called tepals). According to some scholars, it is actually three petals and three sepals (modified leaves).

The basal petal joined to a stamen forms the labellum and takes on a typical appearance depending on the genera such as:


Ciprypedium: shape of a slipper


Cymbidium: boat shape


Phalaenopsis: spur shape


Cattleya: fringed shape

This peculiarity allows pollinating insects to identify the orchid. In fact, the orchid is the zoogamous species par excellence, that is to say it depends exclusively on insects (or other animals) for pollination and this characteristic finds its maximum expression in this large family.

When the flower is in bud, the lip is posteriorly as it blooms, rotates 180 ° so that the lip at the end is in front. This process is known as resupination and is typical of almost all orchids. One exception is the genus Malaxis which undergoes a rotation of 360 ° so that at the end the labellum finds itself in the initial position.

Unlike all the other plant species in the orchid, the stamens and pistils, instead of being separated, are joined together in a single structure called column (or gymnostemium), at the top of which it is located the anther which contains two oval / rounded organs, which contain the pollen gathered in said masses pollinodes. Pollinodes have an adhesive base called slimy which serves to keep the pollinodes attached to the insect until it lands on a flower with a sufficiently adhesive stigma to retain it and therefore cause fertilization.

Under the anther, separated from the rostellum you find it stigma, female organ rich in a thick and sticky liquid which has the function of retaining pollen. Under the stigma is there'ovary female reproductive organ that contains many ova from which the capsule (the fruit) which usually opens according to three slits which will contain numerous snippets seeds (some hundreds of thousands). The seeds are powdery and devoid of endosperm with a rudimentary embryo that needs symbiosis with a fungus to germinate (the seeds germinate very well if invaded by the fungal hyphae of the Rhizoctonia fungus or others also belonging to higher genera).

At this point you will allow my personal digression. Nature is extraordinary and without going far we look at the orchids that to perpetuate their species have devised a series of mechanisms worthy of the greatest strategist. In fact, orchids do not have aerial pollen, i.e. pollen that is carried by the wind, they resort to external help and attract butterflies, flies, hummingbirds, bees. These animals, attracted by the colorful shapes and colors, enter their complex floral structure and involuntarily carry pollen from one flower to another. Some varieties of orchids have specific insects as pollinators for which they have structured their flower "a hoc" for that particular pollinator.

A striking example is the orchid Angraecum sesquipedale (photo below), which has a lip over 30 cm long and the nectar is found in the final part.

This feature was already noticed by C. Darwin who then hypothesized the existence of an insect that had a trunk long enough to be able to reach the nectar. The good Darwin was right, in fact over forty years later it was discovered that a sphinx butterfly had the particularity of having a proboscis (spirotromba) so long that it was called Xanthopan morganii praedicta ("Predicted") in honor of Darwin's genius.

DRUM

The stem or stem has the function of both supporting the plant and acting as an intermediary between the roots and the flower to ensure a constant flow in both directions.

There are orchids with stems and orchids without stems.

Among the ORCHIDS WITH STEM we remember Cattleya, Dendrobium, Phalenopsis, Vanda, Oncidium.

Among the ORCHIDS WITHOUT DRUMS we remember Phaphiopedilum, Pleurothallis and Masdevallia, just to name a few.

In turn, orchids can have the stem that develops:

WITH VERTICAL GROWTH: called stem monopodial (examples are sonophalenopsis, Vanda, Angraecum) with a single stem that grows vertically and has no pseudobulbs.

The flowers grow near the apex between the leaves.

WITH HORIZONTAL GROWTH: called stem sympodial (examples areCattleya, Cimbidium, Dendrobium etc.) which have a kind of rhizome that grows horizontally from which vertical stems called pseudobulbs emerge.

The flowers can sprout or on top of the pseudobulbs (eg. Encyclie) or at their base or by the pseubobulb itself (eg. Erie).

The variability of shape of different orchids in nature is dictated by the fact that they often have to live in extreme conditions. This means that orchids belonging to the same genus have adapted their organisms in extraordinarily different ways. Here are some examples:

Dendrobium cucumerinum (photo below) which has transformed its leaves into sausage species to accumulate water reserves to survive periods of drought.

Dendrobium senile (photo below) whose stem is covered with a thick down that serves the plant to limit transpiration and therefore dehydration.

LEAVES

The leaves can be arranged in various ways in the plant. They are usually alternated in the stem and the shape can be very varied: elliptical, lanceolate, linear, triangular, etc. They are often fleshy and in this case they take on the function of reserve organs for the periods of vegetative rest.

ROOTS

The roots of orchids are different depending on the genus. Let's see in detail:

Orchids with only aerial roots

(epiphytic orchids) that grow attached to trees that they use as a support. The roots are hanging and have the characteristic of having a sort of cap in the terminal part and are covered with a spongy tissue called velamen which, with chlorophyll, photosynthesizes and absorbs water vapor from the atmosphere.

The best known and most cultivated genera of epiphytic orchids are: Cattleya, Vanda, Odontoglossum.

Orchids firm and deep in the ground

(terrestrial orchids) widespread in temperate climates, where the roots are firmly in the earth and through them, the plant absorbs the nutrients.

In terrestrial orchids there are called formations tubercles formed by the welding of some roots that we can find both black when they fed the sprout of the year and white when they are destined to supply nutrients to the sprout of the following year.

Typical examples are: Cymbidium, Cypripedium, Paphiopedilum.

Then there are the intemedie forms which are orchidssemi-epiphytes, plants that live on the branches and trunks of other plants or with lithophytic behavior that live on rocks covered by a thin layer of plant fragments, mosses and lichens that have

roots that are somewhere in between

between the epiphytic and the terrestrial ones.

Classic examples of epiphytes are the Phalaenopsis, Dendrobium, Vanda etc. while for example the Cattleya, it can be epiphytic or semi epiphytic.

Then we remember the orchids that live parasitically

which are those devoid of chlorophyll that lead a heterotrophic life (which feed on organic material present in the environment) such as fungi at the expense of humus or soil materials. Some have fungus-infected roots, others like Corallorhiza they are rootless, their role is assumed by the coral-like ramifications of the rhizome.

Video: Orchid Flower Anatomy