Question: Elymus and Macropidia, are which type of mutual multicellular organisms?

Context paragraphs:
Multicellular organism: Multicellular organisms are organisms that consist of more than one cell, in contrast to unicellular organisms.

Axenic: In biology, axenic describes the state of a culture in which only a single species, variety, or strain of organism is present and entirely free of all other contaminating organisms.  The earliest axenic cultures were of bacteria or unicellular eukaryotes, but axenic cultures of many multicellular organisms are also possible.  Axenic culture is also an important tool for the study of symbiotic and parasitic organisms in a controlled manner.

Abderrazak El Albani: Abderrazak El Albani is a French-Moroccan sedimentologist, Professor at University of Poitiers at the Hydrasa laboratory (IC2MP - CNRS).  He is significant for having discovered the oldest known fossils of multicellular organisms in the 2.1 billion year-old black shales of the Paleoproterozoic Francevillian Group Fossil Formation in Gabon, which shed new light on the origin of multicellular organisms.

Ediacaran biota: The Ediacaran ( ; formerly Vendian) biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms that lived during the Ediacaran Period (ca. 635–542 Mya).  Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.  The Ediacaran biota radiated in an event called the Avalon explosion,   million years ago , after the Earth had thawed from the Cryogenian period's extensive glaciation.  The biota largely disappeared with the rapid increase in biodiversity known as the Cambrian explosion.  Most of the currently existing body plans of animals first appeared in the fossil record of the Cambrian rather than the Ediacaran.  For macroorganisms, the Cambrian biota appears to have completely replaced the organisms that dominated the Ediacaran fossil record, although relationships are still a matter of debate.

Mitochondrion: The mitochondrion (plural mitochondria) is a double membrane-bound organelle found in all eukaryotic organisms.  Some cells in some multicellular organisms may however lack them (for example, mature mammalian red blood cells).  A number of unicellular organisms, such as microsporidia, parabasalids, and diplomonads, have also reduced or transformed their mitochondria into other structures.  To date, only one eukaryote, "Monocercomonoides", is known to have completely lost its mitochondria.  The word mitochondrion comes from the Greek "μίτος" , "mitos" , "thread", and "χονδρίον" , "chondrion" , "granule" or "grain-like".  Mitochondria generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy.

Macropidia: Macropidia fuliginosa, the sole species of genus Macropidia, is a perennial rhizomatous flowering plant.  Commonly known as the black kangaroo paw, it is endemic to Southwest Australia, specifically from Perth to Geraldton in the north of the region.

Elymus (plant): Elymus is a genus of perennial plants with approximately 150 species in the grass family, related to rye, wheat, and other widely grown cereal grains.

Domain (biology): In biological taxonomy, a domain (Latin: "regio"), also superkingdom or empire, is the highest taxonomic rank of organisms in the three-domain system of taxonomy designed by Carl Woese, an American microbiologist and biophysicist.  According to the Woese system, introduced in 1990, the tree of life consists of three domains: Archaea, Bacteria, and Eukarya.  The first two are all prokaryotic microorganisms, or single-celled organisms whose cells have no nucleus.  All life that has a nucleus and membrane-bound organelles, and multicellular organisms, is included in the Eukarya.  Stefan Luketa in 2012 proposed a five "dominion" system, adding two more to the above.

Chemotaxis: Chemotaxis (from "chemo-" + "taxis") is the movement of an organism in response to a chemical stimulus.  Somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment.  This is important for bacteria to find food (e.g., glucose) by swimming toward the highest concentration of food molecules, or to flee from poisons (e.g., phenol).  In multicellular organisms, chemotaxis is critical to early development (e.g., movement of sperm towards the egg during fertilization) and subsequent phases of development (e.g., migration of neurons or lymphocytes) as well as in normal function.  In addition, it has been recognized that mechanisms that allow chemotaxis in animals can be subverted during cancer metastasis.

Ocelloid: An ocelloid is a subcellular structure found in the family "Warnowiaceae" (warnowiids), which are a members of a group of unicellular organisms known as dinoflagellates.  The ocelloid is analogous in structure and function to the eyes of multicellular organisms, which focus, process and detect light.  The ocelloid is much more complex than the eyespot, a light-sensitive structure also found in unicellular organisms, and is in fact one of the most complex known subcellular structures.  It has been described as a striking example of convergent evolution.

Supporting paragraphs: Elymus (plant) Macropidia
Answer: plants