Zamiaceae

Zamiaceae
	Encephalartos villosus , female plant
Systematics
Empire :	Plants (Plantae)
Department :	Vascular plants (tracheophyta)
Subdivision :	Seed plants (Spermatophytina)
Class :	Cycadopsida
Order :	Cycads (Cycadales)
Family :	Zamiaceae
Scientific name
	Zamiaceae
	Horan.

Zamiaceae are a family within the order of the cycads (Cycadales).

description

Encephalartos altensteinii with simply pinnate leaves

Vegetative characteristics

Cycads are very long-lived, mostly evergreen plants.

The leaves of the cycads are simply pinnate leaf fronds that look very similar to fern fronds . Initially, the fronds are often rolled up like ferns. Unlike the similar palm fronds , the leaf veins of the cycads are forked ( dichotomous ). Most of the time, a wreath of new leaves forms at the same time, usually once a year. The older the plant, the more new leaves are formed each year.

The wood of the cycads is rich in mucus ducts and has very broad radial medullary rays ("manoxyle wood"). Just like the conifers , the wood cells have pits . The root center (marrow) is partially rich in starch and serves as a place for storing reserve materials . On the outside, however, there is water-bearing fabric. The roots are often underground. Occasionally, however, there are also above-ground, coral-like-looking ("coralloid") roots in which nitrogen-fixing symbionts ( cyanobacteria of the genera Anabaena , Calothrix and Nostoc ) live. These supply the cycad with nitrate .

Zamia furfuracea , low growing species; the trunk is mainly underground.

They are low plants with underground trunks to tree-shaped plants that can reach heights of 15 to 30 meters. The trunks of cycads are mostly (apparently) unbranched. Only with the formation of fertile leaves ( sporophylls ) does it come to branching at the base of the fertile sections, because the cones are actually special shoot sections. After the seeds have formed, the cones, which are up to 1 meter long, are pushed aside by a side bud.

Generative characteristics

Cycads are dioeciously separated, so there are both male and female individuals ( diocyte ). In the Zamiaceae family, the plants of both sexes have cone-shaped inflorescences .

Encephalartos lebomboensis , cones with ripe, orange-red seeds

The carriers of the ovules are clearly visible in the cycads as the transformation of leaves. In the female individuals of the Zamiaceae genus Dioon , the fertile leaves are reduced to a partly woody, scale-like part of the cone-shaped inflorescence ( see picture in the gallery ), in the genus Zamia they are shield-like, blunt and feltless. The cone is a side shoot axis ( homology ). After the seeds ripen, the cones are topped by a side bud and bent to one side.

The large, orange, red, pink or red-brown seeds have a three-layered seed coat, consisting of a colored sarcotesta, a woody sclerotesta and a membranous endotesta. The seedling has two cotyledons .

Reproduction

Ceratozamia , microsporophylls of the male cone

5 to 1000 pollen sacs are formed on the underside of the scales (= microsporophylls ) of the male cones . The pollen sac wall is multilayered and is divided into an exothecium (outer layer) and a tapetum (inner layer), which then dissolves (plasmodial tapetum ) and serves to nourish the pollen mother cells. The pollen mother cell initially divides into a prothallium cell and an antheridia mother cell . The latter then divides into a pollen tube cell and a generative cell ( antheridial cell ). The finished pollen is therefore three-celled.

The pollination via beetle ( Cantharophilie ) or wind ( anemophily ).

When the pollen reaches the female ovule on the megasporophyll , the generative cell divides into a stem cell, which remains on the prothallium cell, and a so-called "spermatogenic cell". The spermatogenic cell then forms 2 (with Microcycas up to 20) spermatozoids , which are enclosed by the pollen tube cell . The spermatozoids (equivalent to a sperm cell ) are up to 0.4 mm in size and have a spiral band of flagella at one end . The pollen tube cell then grows into a tube, transports the spermatozoids to the archegonia chamber and releases them there. Then fertilization occurs.

The ovules of cycads consist of an integument (seed coat), a nucellus , which forms a multicellular embryo sac ( gametophyte ). The embryo sac forms two to six (in microcycas up to 100) archegonia , each of which produces an egg cell.

use

Some species of cycads are of some economic importance to humans. The use of the strength in the trunk of many cycads can also be taken from the generic name Encephalartos (bread palm fern ), because it means Greek : en = in, on; kephalon = head, brain; artos = bread.

Danger from humans

Cycads (especially the bread palm ferns) are popular plants in botanical gardens , but private collectors also pay a lot of money to get a cycad. Thefts occur again and again, especially with the very rare species. The IUCN red list lists 238 cycads as endangered, including Encephalartos woodii . This species became extinct in the wild and only one male clone was known, so the species cannot be propagated by seeds. There are around 500 cultured individuals of this clone in botanical gardens.

Systematics and distribution

Disjoint distribution of the recent Cycadophyta in the world.

Individual cycads are native to many tropical countries. It is typical of such an old group of plants that the distribution is disjoint. No species can tolerate frost, so the areas are only in the subtropics and tropics.

The Zamiaceae family is divided into two subfamilies with four tribes. This family includes seven to eight genera with 100 to 200 species:

Subfamily Encephalartoideae: It contains two tribes:
- Tribe Diooeae:
  - Genus Dioon (about 11 species)
- Tribe Encephalarteae:
  - Genus Encephalartos - Bread palm ferns (62 species)
  - Genus Lepidozamia (2 species)
  - Genus Macrozamia (38 species)
Subfamily Zamioideae: It contains two tribes:
- Tribus Ceratozamieae: There is only one genus:
  - Genus Ceratozamia (about 16 species)
- Tribus Zamieae: There are only two genera left:
  - Genus Microcycas : The only one species occurs only in western Cuba.
  - Genus Zamia (Syn .: Chigua ): The approximately 79 species are common in the Neotropic.
With some authors, the two genera Stangeria (with one species in South Africa) and Bowenia (with three species in Australia, endemic to Queensland ) of the family of Stangeriaceae are incorporated into the Zamiaceae.