For more than a century, lichens were understood through a single phrase: a partnership between a fungus and an alga, in which the fungus provides shelter and structure and the alga, by photosynthesis, supplies the sugar. The phrase, repeated in textbooks for generations, had the merit of being short and the demerit of being incomplete. Recent work has shown the lichen to be a considerably more crowded community than the two-partner picture allowed, with a second kind of fungus regularly present and contributing, in ways still being clarified, to the structure long credited to the first.
The discovery did not arrive by accident. Researchers attempting to grow lichens in the laboratory found that combining the textbook fungus and alga produced, repeatedly, something that did not look like a lichen — a growth lacking the characteristic surface chemistry, the typical colours, the recognisable form. The puzzle stood for some years before a second yeast-like fungus, distinct from the first, was identified in the surface tissue of many lichen species. When this fungus was included, the artificial growths began, at last, to resemble the wild material. The phrase about two partners did not, on this evidence, capture what a lichen is.
It would be hasty, on the other hand, to leap from the addition of a partner to a portrait of lichens as freewheeling collectives. The second fungus is not present in every lichen, contributes differently across species, and is itself part of a broader microbial community whose role in the partnership is still being worked out by patient laboratory work. The lesson is not that the old picture was wrong in every detail but that its tidiness was an artefact of how lichens were originally studied, and of which organisms the available techniques were able to recover. Once researchers stopped assuming there were two partners and started looking with newer molecular tools, additional partners turned out to be there.
The case is instructive beyond lichens. A category long held to be settled — 'a fungus and an alga' — was settled in part because the available techniques could not see what they were not looking for. The corrective is not a romance of complexity but a habit of suspecting that the simplest available description may have been favoured for reasons of methodology rather than nature. Most settled categories, given new techniques, prove to be busier than they were thought to be.
Which one of the following best captures the main idea of the passage?