Dienstag, 31. Mai 2011

Article of the week - Pollination and reproduction of the higher plants

In this “Article of the Week” I want to talk about the generation of the gymnosperms and the angiosperms and want to give you a general overview about the reproductive organs of plants and how pollination exactly works,

I. General Overview

The most higher species, animal or plant, pass through two different stages of lives: a Haploid and Diploid Stage. In the most cases, living things exist in the diploid stage; that means, they have a duplicated set of chromosomes (e. g. a normal human has 2 x 23 chromosomes). If an individual has more than a duplicated set, we called it Polyploidy.

So, before reproduction, the organism begins to transform its duplicated set of chromosomes into a single set. This process is called Meiosis. During the Meiosis new cells will created but the total number of the chromosomes will not rises. So at the end of the Meiosis, we normally have many “male” and “female” cells with a haploid set of chromosomes.

For example, the sperm cells (male) or the ovum (female) of the animals are haploid cells. Plant will even made an entire, small haploid organisms, which are called Prothallium. In many cases, especially at the higher Plants, the male Prothallia are much smaller than the females and have also different anatomy. In this cases, the male Prothallium is called Microprothallium and the female Makroprothallium.

At the high plants, the female Makroprothallium.is also known as Ovule and the male Microprothallium as Pollen.

II. Anatomy of the ovule
The ovule is the result of many cell divisions. It starts after the Meiosis with a haploid cell: the Mother cell. This cell germinates and is divided into four smaller daughter cells. However, from these four cells only one will survive. This cell will multiply its chromosomes, so in the end, we have a oktoploid (angiosperms) or heptaploid (gymnosperms) cell; the pre-form of the ovule. Later, this pre-form is subdivided into seven smaller cells again; this is finally our ripe ovule.

So the ovule consist of seven different cells. The biggest one is the embryo sack. This diploid cell is later responsible for the nutrition of the embryo. The angiosperms have a diploid embryo sack, the gymnosperms a haploid one (this is a basic difference between the gymno- And angiosperms).
Then, we have the haploid ovum, which is flanked by two helper cells, the synergids. On the opposite side, there are also three other helper cells, which are called antipods.

The ovule is surrounded by a endosperm, which is called the Nucellus. Ovule and Nucellus are protected by one (gymnosperms) or two (angiosperms) layers: the integuments.
At the base, the integuments are often fused. At the top, the integuments are forming a small tube, which is the entrance to the ovule. This entrance is called Micropyle; the fused area is called Chalaza.
Finally, the whole ovule is located at the end of a short stalk: the funicle, which connects the ovule with the placenta.

At the angiosperms, the ovule is enclosed by the ovary, that is formed by the carpels. At the gymnosperms the ovule is free and protected by the seed scales.

III. Anatomy of the pollen

The anatomy of a pollen is more simply than the anatomy of the ovule. It consists of two haploid cells: the “pollen tube mother cell” and the “spermatozoon mother cell”. The first one is responsible for the growing of the pollen tube, the second one for fertilization. They are both enclosed by a callose layer. The surface of this layer can be shaped very differently. For example, some pollens has air filled wings or a very spiky surface.

IV. Pollination

After the polen has landed at the stigma, the “pollen tube mother cell” breaks through the callose layer and grows through stylus and ovary right to the ovule. Here it enters the ovule by the micropyle and grows in the synergids.

After the pollen tube is completed, the spermatozoon mother cell divides itself into two small spermatozoon cells. This cells wander through the pollen tube in the ovule. Here, one spermatozoon enters the nucellus and fuses with its two cores, forming a triploid tissue that is called the secondary endosperm. The other cell enters the ovum and its haploid core fuses with the core of the ovum, what is the fertilization. After successful fertilization, the now diploid ovum starts to grow and becomes the plant embryo. During the first hours of it life, the embryo is feed by the nucellus, later by the secondary endosperm.

The pollination of the gymnosperms is very similar to this process, but here, the pollen is caught by a special drop, that grows through the micropyle. This drop is called the pollination drop. Another different is, that the gymnosperms have no double fertilization. Only the ovum is fertilized by on spermatozoon, the endosperm remains haploid.

Sonntag, 29. Mai 2011

Plant of the Day (May 29th , 2011) - Laburnum anagryoides Medik.

Sorry, but because I was very busy the last days, I was not able to write a new “Article of the Week”. But don't be worried, I will make it tomorrow and post it at Tuesday. It will be about pollination and the anatomy of the ovules.

So, today, I will only post a new “Plant of the Day”. It's the “yellow brother” of Robinia pseudoacacia L., which I've introduced two days ago: Laburnum anagyroides Medik.; in English known as “Golden Laburbum”, “Golden Rain” or “Golden Chain” and as “Gewöhnlicher Goldregen” in German. It also belongs to the Fabaceae family.

L. anagyroides - Habitus

It's a big shrub or tree, that can reach heights until 8 metres or 26,3 feet. The foliage-leaves have a long stalk and are digitate. Every leaf is divided into three small and egg-shaped leaflets. The leaves are dark-green.

The inflorescence is the same as in R. pseudoacacia: a loose, hanging racime with short-stalked, yellow flowers. They are cygomporphic and consist of the typical, different shaped petals of the Fabaceae: “banner”, “keel” and “wings”. The whole sight of the golden-yellow and hanging inflorescences, which gave the plant the name “Golden Rain”.

 L. anagyroides - inflorescences

Originally L. anagyroides is native to Middle and South Europe, but as neophyte and popular garden tree, it can be found everywhere in Europe today. It prefers warm and damp habitats on lime. In Germany, Laburnum anagryoidies Medik. is in the vocation to be very toxic. In fact, the seeds of this species contains cystine, which can be deadly, because it causes respiratory paralysis. But in the most cases, you will puke before this happens, so deaths through “Laburnum” are, in contrast to the vernacular a very rare phenomenon.

Freitag, 27. Mai 2011

Plant of the Day (May 27th, 2011) - Robinia pseudoacacia

So, today’s “Plant of the Day” is a very beautiful, interesting but also sometimes problematical shrub: Robinia pseudoacacia L., the “Black Locust” or “Pseudo Acacia” in English and the “Gewöhnliche Robinie” or “Silberregen” in German.

 R. pseudoacacia - habitus

This plant belongs to the Fabaceae family. It's not the first Fabaceae in this Blog; this was Trifolium medium L., which I've shown you earlier.

R. pseudoacacia is a big shrub or tree, which can reach heights between 15 and 25 metres (or 49 – 99 feet). The leaves are pinnate and each of the grass-green leaflet is egg-shaped. The brown bark is deeply furrowed. It contains coumarin.

 R. pseudoacacia - leaf

Like all species of the Fabaceae, R. pseudoacacia has the typical, cygomorphic flowers of this family with different shaped petals: the “banner”, the “keel” (the two fused bottom petals) and the “wings”. The whole flower is white; the inflorescence is a raceme.

 R. pseudoacacia - raceme and flowers

Originally, Robinia pseudoacacia L. was native to North America, especially to the Appalachian Mountains and the East Coast of the USA. Later it came to Europe as Neophyte spread out very quickly. So today, you can find this species on many different places like gardens, parks but also ruderal wastelands, e. g. at old, abandoned train tracks.

 R. pseudoacacia - habitus

The reason for its high modesty is very simple. As a Fabaceae, R. pseudoacacia is able to fix atmospheric nitrogen through a symbiosis with symbiotic bacteria. So, the species can grow better and faster than its competitor and alsoon the most soils. This is a good but also a problem.

It's a good, because R. pseudoacacia is the perfect plant for renaturing industrial or urban wastelands (for example after World War II, one of the first plants in the ruins of German cities was R. pseudoacacia).

However, this can also become a problem, Because of its competitive strength, R. pseudoacacia can be an invader, which invades Biotopes and displace other species.

Mittwoch, 25. Mai 2011

Plant of the Day (May 25th, 2011) - Iris pseudacours L.

Iris pseudacorus L. (in English known as “Yellow Iris” and in German as “Sumpf Schwertlilie” or “Wasser Schwertlilie) is today's “Plant of the Day”. The species belongs to the Iridaceae family. It's a monocotyledon; that means it as only one cotyledon after germination. The Monocotyledons are a great sub-group of the angiosperms. The Cyperaceae or the Poaceae (grasses) for example are also monocotyledons.

I. pseudacorus - habitus

I. pseudcacorus is a very large flower (80 – 100 cm) with long, sharp-edged and sword-shaped leaves. They are greyish green and have a striking, strong midrib. They are unifacial; that means, that the entire leaf-blade was made by the ventral side of the leaf-primordium. So, you can finde stomatas all over the leaf-blade, which in fact only consists of a ventral side.

Sometimes, the leaves can be confused with the leaves of Acorus calamus L., which also gives the species its name (“pseudacours” means “Fake Acorus). Anyway, the leaves of A. calamus have some strong “side rips” (see the picture in my last “Article of the Week”).

I. pseudacorus - flower

The cygomorphic flowers are yellow and consists of six equal shaped leaves (Tepals). Such a perianth is also called a perigone. There are also three stamens and three carpels (this threefold of the flower is basically a typical character for many monocotyledons).

I. pesudacorus - flower

The plant is native to Eurasia, but can also be found in North America as Neophyte. As you can maybe imagine through my articles about the field trips to Lake Unterbach and Lake Uemmingen, I. pseudacorus grows at marshes, swamps and wetlands. It prefers wet clay soils, but also tolerates a certain height of water.

Montag, 23. Mai 2011

Article of the week - Field Trip to Lake Uemmingen

This weekend I've participated in a field trip to the “Ümminger See” (Lake Ümmingen) in Bochum, Western Germany. The field trip was organized by the “Bochumer Botanischer Verein” (Botanical Association of Bochum; check out Google, because I don't know if linking is allowed) and the “NABU”. It was similar to my field trip to Lake Unterbach two weeks ago but also a little bit different. So, in this “Article of the Week”, I want to give you an overlook of this area.

Lake Ümmingen is located at Langendreer, a urban district of Bochum, a town in Western Germany, which is also part of the famous Ruhr Region (German: Ruhrgebiet), one of Germanys former most important industrial areas. Its current area is about 11 hectares.

Lake Ümmingen was originally a mill pond; later it became a kind of storage pool for the polluted mine water of the coal mine “Zeche Vollmond” (mine “full moon”). After the closure of the mine, Lake Ümmingen was excavated and expanded to become a recreation area.

Basically, today's Vegetation of Lake Ümmingen can be summarized into two main parts: firstly the surrounding vegetation and secondly the shore vegetation. It hast to be said, that the main part of these vegetations is not naturally but planted. Anyway, it's a n interesting mixture of species.

I. Surrounding vegetation of Lake Ümmingen

a) General overview

The surrounding vegetation is dominated by high or medium high scrubs and also meadows. Here we find some very typical species of this vegetation types, although not all of them are native to Germany.

The following list will give you an example of the species, you can find in the surrounding area of Lake Ümmingen.

b) List of species (sample)

Corylus columa L.
Phalaris arundinacea L.
Alopecurus pratensis L.
Epipactis helleborine (L).Crantz.
Geranium dissectum L.
Cornus sanguinea L.
Cornus alba L.
Persicaria amphibia (L.) Delarbre
Glechoma hederacea L.
Rubus macrophyllus Weihe & Nees
Rubus caesius L.

c) Gallery
Persicaria amphibia (L.) Delarbre (land form)

Phalaris arundinacea L.

Alopecurus pratensis L.

Cornus sanguinea L.

Epipactis helleborine (L).Crantz.

II. Shore vegetation of Lake Ümmingen

a) General overview

The majority of the lake shore (especially the north shore) was created artificially; that means the shores were fortified with concrete walls, which makes it difficult for a natural vegetation. Anyway, at the south shore, you can find some exception; especially the small still waters with its reeds.

b) List of species (sample)

Iris pseudacorus L.
Juncus compressus Jacq.
Populus x canadensis Moench.
Salix alba ssp. Vitellina L.
Atriplex prostrata C. D. Bouche ex. DC.
Typha angustifolia L.
Calystegia sepium (L). R. Br.
Schoenoplectus lacustris (L.) Palla
Acorus calamus L.
Quercus palustris Muenchh.
Pulicaria dysenterica (L.) Bernh.
Juglans regia L.
Phragmites australis (Cav.) Trin. Ex Steud.
Typha latifolia L.
Heracleum mantegazzianum Somm. & Lev.
Matteuccia struthiopteris (L.) Tod.
Inula helenium L.
Hypericum perforatum L
Bromus inermis Leyss.
Amoracia rusticana G. Gaertn, B. Mey. & Scherb.
Rosa multiflora Thunb.
Carex hirta L.

c) Gallery
Inula helenium L. (look at the white nerve)

Matteuccia struthiopteris (L.) Tod.

Phragmites australis (Cav.) Trin. Ex Steud.

Populus x canadensis Moench.

Quercus palustris Muenchh.

Schoenoplectus lacustris (L.) Palla

Typha latifolia L

Acorus calamus L.
Atriplex prostrata C. D. Bouche ex. DC.

Freitag, 20. Mai 2011

Plant of the Day (May 21st , 2011) - Aesculus hippocastanum L.

Because I will be very busy today, I will present today's “Plant of the Day” article a little bit earlier. It is Aeculus hippocastanum L., a very impressing and beautiful (for me at least) tree from the family of the Sapindaceae and the sub-family Hippocastanoide. I'm really sure, the most of you know this tree or have seen it before. In English, it's known as “conker tree” or “horse chestnut” and in German as “Gewöhnliche Rosskastanie”.

A. hippocastanum - habitus

It's a tall tree, which can reach highs about 25 metres (82 feet). The leaves are digitate and very large. The single leaflets are inverted egg-shaped. There are between five and seven leaflets. The also large flowers are sitting into a upright panicle as inflorescence. Their petals are white with a red, yellow or purple spot at the base.

A. hippocastanum - flowers

A. hippocastanum - leaf

Horse chestnut” is probably best known for its fruits: the chestnuts. These are spiky capsules with the typical brown seed with its white and large hilum. The looks similar to the fruits of Castanea sativa Mill. but unlike to this species, the fruits are inedible.

A. hippocastanum - flowers

Originally the species is endemic to the Balkan region (e. g. Greece, Albania or the Republic of Macedonia), where it grows in shady, fresh ravine forests with neutral or slightly alkaline soils. However, it has also become very popular as park or garden tree, so you can find it in all over Middle Europe today.
A. hippocastanum - flowers

Donnerstag, 19. Mai 2011

Plant of the Day (May 19th, 2011) - Carex elongata L.

Carex elongata L. is the second species of the Genus Carex, which you can find in the wetland area at Lake Unterbach in Düsseldorf, Western Gemany. In Germany, we called it the “Langjährige Segge” oder “Walzen-Segge”. Unfortunately I haven't found an English translation, but the Latin name means something like “Stretched Sedge”.

 C. elongata - flowers

In contrast to Carex nigra (L.) Reichenbach, Carex elongata L. belongs to the sub-genus Homostachyae. That means, female and male ears are not differently shaped

 C. elongata - flowers

Its a small, grass-like herb with highs between 30 and 60 centimetres. The leaves are grass-green and very long. They are located only at the ground of the triangular shoot-axis. Unlike at C. nigra, the stomata are located at the underside of the leaves.

 C. elongata - leaves

The flowers forming an ear-like inflorescence. This ears are less dense at the base, that means, here the single flowers are not so close together. That gave the species also its name (elongata means “stretched”). They shimmer also brownish.

C. elongata - flowers

Like C. nigra, C. elongata is a typical plant for wetlands, marshes or swamps. It prefers places with a very wet and nutrient-poor soils. It native to Europe but can also been found in Western Asia.

Dienstag, 17. Mai 2011

Plant of the Day (May 17th, 2011) - Carex nigra (L.) Reichard

In the Article about my small field trip to Lake Unterbach, I shown you a picture of Carex nigra (L.) Reichard. Now it's time, to get closer look on this species.

 C. nigra (L.) Reichard - ears
(male: brown; femal: blackgreen)

Carex nigra (L.) Reichenbach belongs to the Cyperaceaeae family. It's a grass-like herb and between 10 and 40 centimetres high with long, narrow leaves, which has a grey-green top and a dark-green underside. They are sitting in dense clumps.

The leaves are also epistomatic, that means, that the stomata are located at the top of the leaves. This also the reason, why the leaf-top is grey-green.

C. nigra (L). Reinhard - leaves
(look a the white lines of stomatas)

The flowers are sitting in ear-like inflorescences.

C. nigra (L.) Reinhard - flowers

The Genus of Carex is divided into three sub-genera: the Heterostachyae, the Homostachyae and the Monostachyae, what depends on the shape of the ears. C. nigra belongs to the Heterostachyae sub-genus, because the ears with the male flowers differs from the ears with female flowers.

The most two male ears are located at the top of the floral axis. They are brown, black or dark-purple. The 2 - 4 female-ears sitting at the middle of the axis. They are dark-green and have black chaffs.

C. nigra (L.) Reinhard - male ears (brown)
at the top and female ears (dark green) in the middle

C. nigra is widespread in almost the entire, northern hemisphere (Europe, Asia, North Africa and North America). It grows at acid, wet places like swamps, wetlands or floodplains. The species prefer nutrient-poor soils.

The Cyperaceae look similar to the common grasses (Poaceae), but there are some differences between Cyperaceae an Poaceae.

1) Shape of the Shoot axis: First, the Cyperaceae have a triangular shoot-axis without any nodes; the Poaceae on the other side have a round shoot-axis with nodes.

2) Interior of the shoot-axis: The shoot-axis of the Cyperaceae is filled out by marrow; the shoot-axis of the Poaceae is hollow.+

Sonntag, 15. Mai 2011

Article of the week - Inflorescences

The sum of all flowers of a plant is called inflorescence. Inflorescences exist in many different forms and shapes, so in this week's “Article of the Weel” I want to show the basic and common variants of inflorescences. I'll not show all of them, but only the main types.

So first, let us check out some basic terms. When you look at an inflorescence, you have maybe noticed, that some of them are ending into a terminal flower and others not. In Botany we speak of a monotelic (closed) inflorescence in first case and of a polytelic (opened) inflorescence in the second

It's also makes a different, if an inflorescence only consists of single flowers or in turn are compounded of small inflorescences by itself. First we look at inflorescences, which consist only of single flowers.

I. simple Inflorescences

a) ear: the ear is possible the most simple type of an inflorescence. Here, the flowers are sitting directly into the axil of their bracts. Ears can be found at some species of the Poaceae (e. g. the Genus of Hordeum), but also at the Genus Plantago. A cone is also a variant of an ear.

b) raceme: the raceme is not very different from the ear. The only difference is, that the flowers of a raceme are sitting at the end of a short stalk, growing from the axil of a bract. This type of inflorescence can be found e. g. at the Genus of Viccia.

c) umbel: At the umbel, the flowers also are sitting on a stalk. All stalks starts at the same point of the shoot axis. The bracts of the flowers often forms a such called involucrum. So the whole inflorescence looks like a umbrella. Umbels are the typical character for the Apiaceae family, which is also called Umbeliferaceae. Be careful, because sometimes, a raceme is formed like an umbrella (e. g. at Capsella bursa-pastoris L.), but this are no real umbels, because here the stalks are not starting at the same point.

Sometimes, an umbel consists of smaller umbels. This is a double-umbel (d)

e) & f): catkin: a catkin in basically no more than an inverted and hanging ear or raceme. This type of inflorescence is typical for many genera of our native trees like Alnus, Populus or Salix.

note: in this picture the small bracts of 
the spadix and the head 1 has not be draw

g) spadix: A spadix is a special type of an ear, but here, the floral axis is thickened and cylindrical. Spadices can be found e.g. at Zea mays L. (corn) and the most species from the Araceae. They are also typical for the Genus Typha (bullrush or corndog grass) of the Typhaceae.

e) head 1: The first type of the head-formed inflorescence is similar to the spadix. The transition is fluently indeed. The flora axis is also thickened but more jolted. This inflorescence is typical for the Trifolium Genus (e. g. Trifolium medium ssp. medium L. in this Blog)

f) head 2: The second head inflorescence is the characteristic inflorescence of the Asteraceae family (with species like common daisy, common dandelion or the sun flower). Here the floral axis is compressed even more than the first head type. The flowers are sitting directly at this floral axis and their bracts are forming a involucrum.

II. compounded inflorescences

O.k. Folks, now it becomes complicated. In the previous inflorescences we always have a single flower per bract. But sometimes, a inflorescence is multi-branched, that means instead of a flower it has smaller floral axis, growing out from the axial of the bracts.

In this case it depends on how the inflorescence is branched. First, we have two basic types again: the panicle and the cyme.

a) panicle: At a panicle, a new floral axis grows from a single bract. This axis can be branched by itself. The branching doesn't follow a strict scheme and flowers can grow everywhere. A panicle is always monotelic.

b) cyme: If the successive branches follows a scheme, we speak of a cyme. If there is only one new axis per branching, we call it a monochasium. With two new axis per branching, we called dichasium.

Now we subdivide the monochasial and dichasial cymes into three types again.

c) thyrse: A thyrse is simply a inflorescence with dichasial cymes as branches. The inflorescence of Aesculus hippocastanum L. (conker tree) is a good example for a thyrse

d) depranium: A depranium is a monochasial cyme. Here, the floral axis are helical applied towards the main axis.

e) rhipidium: The rhipidium is basically the opposite of the depranium. The successive floral axis grow in a zigzag pattern. The inflorescence of the tomato is e. g. a rhipidium.