Why is sequoia (the tree) not a proper noun? Why is it not capitalized?
A noun is proper if it describes either a single object: the Sun, Asia, Peru or if it describes a specified person - if you say for example Peter- you mean one person not all people who share this name. If you say seqoia I do not know which of many trees you are talking about. That is why seqoia or other names of plants and animals are not proper nouns.