Lords and ladies (also called wild arum and too many other names to bother listing) normally thrive in woodland. Like other flowers which prefer this environment, such as bluebells, they get their main growth and their flowering over early in the year, before the trees have grown the leaves which grab all the sunlight, leaving ground level in permanent semi-shadow.
Quite often the leaves of lords and ladies have this black mottled effect. A quick web search showed just about every web page about the plant mentioning this effect, but none giving any hint about the cause. Is it natural variation, or perhaps the result of a common viral infection?