Last summer, my two young nephews came to stay for a few days at my place in the country (well, it’s “country” to them, as it has a garden and is not completely surrounded by concrete). Wishing to encourage their interest in natural history, I asked them what they had seen on their walk one morning. They said they had seen “flowers”. What sort of flowers? “Don’t know,” they said. Well, what were they like? “Yellow”, they said.

A quick run through my (admittedly shaky) knowledge of the likely local flora produced an annotated list of suspects:

1. The meadow buttercup and yellow loosestrife both have flowers with five petals and both have hairy stems. One difference between them is that loosestrife has leaves in pairs while buttercup leaves are alternate.
2. The marsh marigold, with its five petals and alternate leaves, looks a bit like a buttercup, but has a smooth stem.
3. Tufted loosestrife, confusingly, is yellow, but unlike the real yellow loosestrife it has smooth stems and flowers with many (more than five) petals. Like all loosestrifes, however, it has leaves placed opposite one another in pairs.
4. The greater celandine is another flower easily confused with the buttercup, but it has only four petals and its stem is noticeably branched. Yellow wall rocket is likewise branched and has four petals, but its leaves are placed alternately rather than in pairs like those of the celandine.
5. Prickly lettuce is easily distinguished from wall rocket, despite having a branched stem and alternate leaves, because its flowers have many petals.

Armed with a list of “things to look for”, they were sent out to retrace their walk and note the distinguishing features of the flowers they had seen. They jotted down some comparisons between four specimens. At least one of the specimens had five petals. The second and third specimens had identical leaf placement and stem types, but different numbers of petals. The first of the four specimens had a branched stem and more petals than the second. The fourth and last specimen was definitely not the same species as the first, because it had a different leaf placement.

Given that all of their flowers were indeed on my list, what did they find?