1 The sun's rays are strongest during the hours of 10 a.m. to 4 p.m. The sun's rays are also stronger at higher altitudes and lower latitudes (closer to the tropics). Reflection off water, sand, or snow can make the sun's burning rays stronger.  Sun lamps can cause severe sunburn.
Marchantia polymorpha, sometimes known as the common liverwort or umbrella liverwort, is a large liverwort with a wide distribution around the world. It is variable in appearance and has several subspecies.
References in periodicals archive ? The leafy and simple thalloid liverworts have quadrilobed sporocytes, whereas the sporocytes of complex thalloids are generally unlobed. The complex thalloid liverworts (Marchantiopsida) are an early divergent and highly evolved group of organisms. Such pre-meiotic bands of microtubules have been reported in deeply lobed, polyplastidic sporocytes of both simple thalloid (Brown & Lemmon, 2004, 2006) and leafy (Brown & Lemmon, 2009) liverworts.