Isoetes

See quillwort ( Isoetes lacustris ) (A) Whole plant - (1 ) leaf base with sporangium at the base and ligule about - (2 ) longitudinal section and (3) cross -section of the sheet substrate with the chambered sporangium - (4 ) cross-section through shoot base

(Written Isoetes, Isoetes also ) The Brachsenkräuter are the only extant genus of plants of order Brachsenkrautartige ( Isoetales ) within the class Bärlapppflanzen ( Lycopodiopsida ). This perennial herbaceous plants grow with bulbous stem axis submerged in water or on moist soil and are found almost worldwide.

Description

Vegetative characteristics

The Brachsenkräuter grow as a perennial herbaceous plants and have a bins -like habit; in this they differ from all other Bärlapppflanzen.

Sprossachse

The Brachsenkräuter have a short, fleshy, erect tuber as stem axis. The shoot axis is rare once or twice branched dichotomously, these species were formerly placed in its own genus Stylites. The tuber grows underground. The meristem at the upper end is suppressed. The tuber is two, more rarely three-lobed, rather globose to horizontal spindle-shaped.

The shoot axis has a secondary growth. This is done via a more or less Kambiumzone isodiametric cells which results in the tuber of the primary vascular tissue. This cambium forming xylem and phloem little, but a lot of bark tissue. In species of the temperate zones, the cambium is active seasons - dependent. Simultaneously with the formation of new tissue, the outermost fabric zone is rejected together with the leaf residue and roots. Therefore, the mature tuber maintains a constant size.

The primary xylem consists of more or less isodiametric tracheids. At the lower end of the pillar to form an anchor- shaped branch, which lies in the same plane as the transverse slot at the base of the bulb. The output from the cambium to the inside tissue differentiates into a mixture of tracheids, sieve and parenchyma. The discharged to the outside tissue is parenchymatous. A delimiting the vascular tissue endodermis is absent in the Brachsenkräutern.

Root

The lower meristem is also suppressed and lies in the cross column of the tuber. The roots spring from the bottom of the bulb near the meristem. The roots have a single vascular bundle, which is surrounded by a two-layered cortex: the outer one is quite resistant, the inner is made of fine-walled cells, and numerous air-filled intercellular spaces.

Each of the side branches bears at the top of a clump of quill - like leaves ( Mikrophyllen ). The Mikrophylle wear a ligule. The leaves are 1-70 cm long and starts with young plants in two rows ( distich ), this soon goes into a tight spiral around the meristem above.

The leaves are traversed by a single vascular bundle, which is often very thin. Around the vascular bundles are four air channels, which are interrupted at intervals by transverse walls. For aquatic plants, the air ducts are particularly pronounced. The leaf base is broadened and free from chlorophyll. The bases overlap and form a tuft.

Proliferation and gametophyte

The Isoëtales are heterosporous. The sporophylls are not significantly different from sterile leaves. The leaves in the growing season, the first-formed form Megasporangien that later microsporangia, the last-formed leaves are often sterile. The sporangium is formed between ligule and axle. A portion of the tissue in the interior of the sporangium remains sterile and forming partition walls, so-called trabeculae. The mature sporangium is enclosed by a thin shell, the velum. The velum is formed below the ligule and grows over the sporangium, with a central opening, the foramen remains free.

In a megasporangium about 100 mega spores are formed in size from 0.2 to almost 1 mm. In microsporangia of up to one million microspores up to 40 microns in diameter. The microspores are monolet, only have a scar separation, while megaspores are trilet, have a three-rayed stigma. Isoetes is thus the only extant genus of Bärlapppflanzen that form monolete spores, but also one of the very few plants that form both mono-and trilete spores to an individual.

The spores are released only during the decomposition of the sporophyll. Germination and development of the gametes are similar to the moss ferns in the. In contrast, the male gametophyte remains completely in the spore ( endospore is ). Go from the single antheridium produce four spermatozoids, which are vielgeißelig in contrast to those in the moss ferns and Lycopodium. The spermatozoids are released by rupture of the microspore wall. The female gametophyte is similar to the moss ferns. The cell formation reaches far into the interior of spores inside, a diaphragm as with many moss ferns missing. The development of the female gametophyte first runs endospore, but the growing gametophyte tears the megaspore on along the three-pointed scar. However, he makes no chlorophyll. The archegonia are also similar to those of the moss ferns, her neck is, however, of four cell layers, not two.

The first division of the zygote is slightly wrong. It is not formed suspensor, the embryo is still endoscopically, since the outer cell forms the base, all of the rest of the embryo is derived from the remaining inner cell. The embryo rotates during growth, so that it has finally to the top of the gametophyte. He breaks out of the gametophyte, the young plant remains for some time by a sheath of gametophyte tissue surrounded.

From triploid species of Isoetes apogamy is known. Frequently asexual reproduction occurs by budding before instead of the sporangium.

Systematics and distribution

Isoetes is the only tart occurring genus of order Isoëtales. The earlier Stylites calculated species are now expected to Isoetes.

The genus Isoetes comprises about 150 species. Only the lake quillwort and Stachelsporige quillwort occur as rarities in Central Europe. In Europe, North Africa and the Middle East there are the following types:

• Isoetes anatolica Prada & Rolleri
• Isoetes azorica Durieu ex Milde, occurs only in the Azores.
• Isoetes Boryana Durieu, occurs only in France.
• Isoetes creussensis Lazare & P. Riba
• Isoetes duriei Bory, is found in the Mediterranean area.
• Igelsporiges quillwort ( Isoetes echinospora Durieu ), occurs in Europe, East Asia, North America and Greenland and is naturalized in Siberia.
• Isoetes fluitans M.I.Romero
• Isoetes gymnocarpa ( Gennari ) A. Brown
• Isoetes heldreichii Wettst. , Occurs only in Greece.
• Isoetes histrix Bory, is found in the Mediterranean region and in Western Europe.
• Isoetes Iapygia Ernandes & al.
• See quillwort ( Isoetes lacustris L.), occurs in Europe, in Western Siberia, Japan, North America and Greenland.
• Isoetes libanotica Musselman, Bolin & R.D.Bray
• Isoetes malinverniana Cesati & De Not. , Occurs only in North-West Italy.
• Isoetes olympica A.Braun, occurs only in the Middle East.
• Isoetes Sabatina Troy & Azzella
• . Isoetes setacea Lam, ( syn.. Isoetes delilei Rothm ), occurs only in France, in Spain and in Portugal.
• Isoetes sicula death. ( Syn: Isoetes histrix var subinermis Durieu )
• Isoetes todaroana Troy & Raimondo
• Isoetes velata A.Braun ( Syn: Isoetes Boryana Durieu ), with several subspecies, occurs in the western Mediterranean region and in Portugal.

Other types are (selection):

• Isoetes andicola ( Amstutz ) LDGómez ( Syn: Stylites andicola Amstutz ), occurs in the Andes of South America.
• Isoetes biafrana Arthur Hugh Alston, known only from Moka and Oku- Lake
• Isoetes cubana Engelm. ex Baker
• Isoetes mexicana Underw.
• Isoetes sinensis Palmer
• Isoetes tegetiformans Rury