Palmophyllaceae

Palmophyllaceae
Palmophyllaceae
Systematics
Domain : Eukaryotes (eukaryota) Prasinophytae Chlorophyta Class : Palmophyllophyceae Order : Palmophyllales Family : Palmophyllaceae
Scientific name of the  order
Palmophyllales
Zechman et al. 2010
Scientific name of the  family
Palmophyllaceae
Zechman et al. 2010

The Palmophyllaceae are a family of benthic (bottom living), marine (living in the sea) green algae with multicellular thalli . They live mainly in greater depths of the sea and other poorly exposed habitats. The group has attracted scientific attention because it evidently evolves into multicellular cells independently and converges to that of the other green algae and the "higher" plants ( Charophyta ).

features

The algae form leaf-like grass to dark green thalli with a diameter of up to 10 centimeters and a thickness of approx. 2 millimeters. These are either attached directly (genus Verdigellas ) or with a small stalk (genus Palmophyllum ) to hard substrates on the seabed. They form irregular, upright lobes or crust-like to pillow-like coatings. The thallus is gelatinous in Verdigellas , and leather-like solid in Palmophyllum . When viewed microscopically, individually seated spherical cells with a diameter of 6 to 10 micrometers can be seen in this matrix , which are irregularly distributed but somewhat compacted close to the surface. The cells, which are not differentiated from one another, have a single, very large, cup-shaped chloroplast without pyrenoids . The cell nucleus , a mitochondrion and a large Golgi apparatus can be seen inside the cup . The chloroplast is surrounded by two membranes, it contains the chlorophylls a and b, whereby the proportion of chlorophyll b is very high. The accessory pigments siphonein and siphonoxanthin , which are typical for other green algae adapted to low light intensities, are missing. Flagellated or other mobile cells or stages are not known.

distribution

The species of the family live on the seabed of warm seas of tropical latitudes, one species ( Palmophyllum crassum ) also in the Mediterranean . They are known in water depths of around 20, but mostly from over 80 to over 200 meters. The deposits at shallower depths are exclusively in weakly exposed, shaded habitats. On the continental shelf at a depth of 100 meters, the typical habitat of the Verdigellas genus , the relative light intensity is only 0.05 percent of that at the water surface.

Taxonomy and Phylogeny

The family includes six species in three genera. In addition to the genera Palmophyllum with two species and Verdigellas with three species, the rarely found genus Palmoclathrus with the only species Palmoclathrus stipitatus most likely belongs here. Because of their isolated position, they are the only group to be placed in their own (thus monotypical ) order Palmophyllales.

More recent phylogenomic analyzes (investigations of the relationship based on the comparison of homologous DNA sequences) have shown that the Palmophyllaceae are unexpectedly very basal within the Chlorophyta . They are not closely related to the so-called "core chlorophyts", which contain the other groups of multicellular algae, sometimes with a very similar morphology. They group together with a large group of almost exclusively single-celled, planktonic algae, the " Prasinophytae ". These have long been viewed as a kinship group. It later turned out to be a paraphyletic summary of basal chlorophytes. In fact, they are not closely related to each other, but their similarity is based on their common primeval features. One of the orders of the previous Prasinophytae, the Prasinococcales, turned out to be the sister group of the Palmophyllales . The common clade was newly described as the genus Palmophyllophyceae in 2016 . Your sister group is therefore all other Chlorophyta taken together.

This discovery sheds new light on the evolution of multicellularity in the plant kingdom, because it is the most basic group of plants to date that have produced multicellular representatives. Multicellular algae are known from a large number of other different groups, each of which has developed this property many times independently of one another.

Individual evidence

1. ↑ Antoine DN N'Yeurt & Claude E. Payri (2007): Marine Algal Flora of French Polynesia. III Chlorophyceae (green algae). Cryptogamie, Algologie 28 (1): 3-88.
2. ↑ ^{a b} Frederick W. Zechman, Heroen Verbruggen, Frederik Leliaert, Matt Ashworth, Mark A. Buchheim, Marvin W. Fawley, Heather Spalding, Curt M. Pueschel, Julie A. Buchheim, Bindhu Verghese M. Dennis Hanisak (2010): An unrecognized ancient lineage of green plants persists in deep marine waters. Journal of Phycology 46: 1288-1295. doi : 10.1111 / j.1529-8817.2010.00900.x
3. ↑ Palmophyllaceae in AlgaBase Guiry, MD & Guiry, GM 2016. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org ; accessed on May 18, 2016.
4. ↑ Frederik Leliaert, Ana Tronholm, Claude Lemieux, Monique Turmel, Michael S. DePriest, Debashish Bhattacharya, Kenneth G. Karol, Suzanne Fredericq, Frederick W. Zechman, Juan M. Lopez-Bautista (2016): Chloroplast phylogenomic analyzes reveal the deepest Branching lineage of the Chlorophyta, Palmophyllophyceae class. nov. Scientific Reports 6, Article number: 25367. doi : 10.1038 / srep25367 (open access).
5. ↑ Emma Marris: Strange seaweed rewrites history of green plants. Ancient alga developed large size and complex structure independently of other plants. Nature News, May 9, 2016 online
6. ↑ James G. Umen (2014): Green Algae and the Origins of Multicellularity in the Plant Kingdom. Cold Spring Harbor Perspectives in Biology 6: a016170. doi : 10.1101 / cshperspect.a016170