What's an accessory cloud? This is a cloud that accompanies another. Believe me, you would rather see the picture than have one coming at you.
The new accessory cloud is called a “flumen” and is a low cloud associated with severe supercell storms. They move towards but are not attached to thunderstorm clouds, (cumulonimbus), carrying warm wet air. They feed the storm, sometimes supplying enough moisture and energy for tornado development.
Feeding the storm: : A Flumen cloud Source: WMO, International Cloud Atlas
Five other new clouds are "special" clouds which are weirdly-created Frankenstein clouds that are unusually made. Instead of forming due to the humidity and temperature variations in the upper atmosphere, these clouds are created by conditions on the Earth’s surface or conditions created by living organisms. Their Latin names are truly intimidating mouthfuls. Two are:
Cataractogenous, describing clouds that develop from the spray of large waterfalls, and
Flammagenitus, describing clouds formed by wildfires.
Water and fire clouds: Cataractogenous and Flammagenitus clouds are created by surface conditions. Source: Wikipedia
Living things can create clouds as well. One, newly recognized, is Silvagenitus, clouds formed under the influence of moisture from respiring trees. The woodlands carry moisture from their roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. You can see it rising like steam and forming clouds.
Silvagenitus, the forest clouds Source: WMO, International Cloud Atlas
Two types of special clouds are made by man:
homogenitus, describing clouds formed by human activities, such as airplane contrails and power plant steam, and
homomutatus, describing clouds originally made by humans that gradually transform into more natural-looking forms, like a contrail that eventually spreads in the wind.
The clouds we make: Homogenitus (Source: Wikipedia) and Homomutatus (Source: WMO, International Cloud Atlas)
Those are all for now. Keep your cell phones out. The next new clouds could be discovered by you!