Moss: Suspected to be one of oldest multicellular organisms.

A moss spreading throughout the Hawaiian Islands appears to be an ancient clone that has copied itself for some 50,000 years—and may be one of the oldest multicellular organisms on Earth, a new study suggests.
The peat moss Sphagnum palustre is found throughout the Northern Hemisphere, but the moss living in Hawaii appears to reproduce only through cloning, without the need for sex or production of spores
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 Fossilized S. palustre moss remains have been found in 23,900-year-old peat near the summit of Kohala Mountain on Big Island (Hawaii).

From these remains, Karlin and colleagues inferred that the moss had been in Hawaii at least that long, and perhaps longer.
To find out, the team analyzed the genetic diversity of the current population of moss on the island and determined a mutation rate. Using this mutation rate, they estimated how long it took for the different moss populations to get to where they are genetically—about 50,000 years.
The genetic analysis also revealed surprising diversity—challenging the popular assumption that clones are genetically drab because they can't swap DNA through sex.
"They're not identical because mutations are always occurring," Karlin said. "So given a sufficient period of time, you will find that offspring from a clone may be genetically different from one another."
"However, there are probably other plant populations on islands having a similar history that we haven't studied yet."

Above was take  from National Geographic website