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> Living off others means genes not needed:
> 
> https://www.quantamagazine.org/dna-of-giant-corpse-flower-parasite-surprises-biologists-20210421/
> 
> "More than a decade ago, Rafflesiaceae parasites caught the eye of Jeanmaire Molina, an evolutionary plant biologist at Long Island University in Brooklyn, who wondered if their genomes were as bizarre as their outward forms. Her initial investigations suggested they were. As she and her colleagues described it in a 2014 paper in Molecular Biology and Evolution, they successfully assembled the mitochondrial DNA from one Philippines species of Rafflesia. But they were unable to detect any functional genes from its chloroplasts. The plants seemed to have simply ditched their entire chloroplast genome.
> 
> ***
> 
> "This shocking finding has now been confirmed by an independent research team from Harvard University. The draft genome for another member of the Rafflesiaceae family that they recently published in Current Biology is full of surprises, showing how far parasites can go in shedding superfluous genes and acquiring useful new ones from their hosts. It also deepens mysteries about the role of highly mobile genetic elements that don’t encode proteins in enabling evolutionary changes. Perhaps the greatest lesson of the study is how much we still have to learn about genomics, particularly in plants, and in parasites — a category of organisms that includes more than 40% of all known species.
> 
> ***
> 
> "Sapria’s genome follows several trends seen in many other parasitic plants (and in parasites more generally). Like them, Sapria has done away with many genes considered essential to its free-living relatives. Because parasites steal from their hosts, they essentially outsource the labor of metabolism, so they don’t need all the moving biochemical parts of an independent plant cell.
> 
> "Still, Davis was shocked to see that nearly half of the genes widely conserved across plant lineages had disappeared from Sapria. That’s more than twice as many genes as are lost from the parasitic plants called dodders (genus Cuscuta), and four times the losses in cereal-killing witchweeds (genus Striga). “We knew that there would be loss,” he said, “but we didn’t think it would be on the order of 44% of its genes.'”
> 
> Comment: Life requires the information in genes to function properly. If the host plant is doing most of the work, shucking unneeded genes is a logical result.