Meatshrooms are gengineered mushrooms; the fruiting bodies of fungi that have been designed to have the taste, texture, and nutritional qualities of animal flesh if they are cooked, or in some cases even if they are still raw. They are of ancient derivation; meatshrooms first became widespread during the Interplanetary Age, and have formed a part of the diet of many a human, as well as of many other omnivorous or carnivorous biont Terragen clades, ever since.
Meatshrooms were part of the second wave of gengineered innovations from baseline fungal stocks, following on some more moderately gengineered varieties that had been slight adaptations of baseline species. Meatshrooms were intended to provide a replacement or alternative for animal foods. This proved easier to accomplish in fungi than in plants, since many fungal fruiting bodies already had some meat-like traits. For instance, the "ox tongue" mushroom in its baseline form tastes remarkably like liver when cooked and Asian cuisine had a long tradition of producing meat-like dishes from various other fungi. The gengineers hoped to meet culinary demand for meat products without the high costs and ethical and legal issues of intensive meat production from entire animals or the costs of support structures for tissue cultures. They also intended that the fungi be integral to waste management systems in the increasingly crowded cities of Earth and the tightly cycled artificial ecosystems of the new orbital habs and other extraterrestrial colonies.
Unfortunately, meatshrooms did not prove as popular as their designers had hoped. Earlier gengineered mushrooms had been seen as an improvement on baseline mushroom varieties, whereas meatshrooms were seen as second-rate meat; most people tagged them as a poverty dish ("plebfood" in the language of the day). True animal products became the domain of the rich, and eating them a status symbol. In addition, the fact that they were grown on processed sewage and garbage caused people to regard them as unsafe and unclean "sewerfood". This had some basis in fact. On occasion the feedstock contained unhealthy biotoxins or heavy metals, or the fruiting bodies accidentally came in into contact with the underlying nutrient base. Sometimes, too, new varieties were put on the market without proper testing, or were accidentally hybridized with fungi intended to produce industrial or pharmaceutical products. Lastly, as often happens with baseline mushrooms, overgrowths by toxic or unpalatable fungi or bacteria made meatshrooms dangerous or inedible. These rare but very real hazards did not help public perception. For most of the Interplanetary Age meatshrooms were widely cultivated but were a second class and second choice food in the eyes of most persons. The final blow against the popularity of meatshrooms was the development of deliplants. These provided all the advantages over actual animal products of meatshrooms, but had an attractive appearance and had the advantage in terms of perceptions in that they came from gardens and orchards and not waste heaps and sewage processing plants.
The Nanodisaster changed this balance. Most societies that survived the Nanodisaster did so by carefully screening themselves from outside contact, or were simply isolated due to the breakdown of trade and travel. As a consequence they observed very tight cycling of nutrients in the surviving settlements. Under these circumstances, eating animals of any kind was seen as an extravagance, and wasting potential food production of any kind was simply untenable in practical terms. Over the long years of the Nanodisaster and subsequent dark ages, cultures changed to meet this reality, and meatshrooms (together with a wide variety of other fungal products) came to be a deeply traditional and much beloved part of most cuisines.
In the present day, there are dozens or hundreds of varieties of meatshroom available in any given culture, and hobbyists still tinker to produce new varieties for local consumption. However some of the classic varieties first produced by Third Kingdom Corporation in the days of the Gengineer Republic are still popular.