Caspar Edwardian Botanistexplorer In China Hunting Plants Meets Eurasian Beauty

I would love to find and re-read this book, but I need your help. It's a large format Harlequin published sometime in the '80s, I think. The author had written for Harlequin Presents before coming out with this large-format historical.The story is set in EDWARDIAN ENGLAND AND CHINA. Caspar, an English nobleman (duke?) is a BOTANIST, EXPLORER AND PLANT-HUNTER who MEETS A YOUNG HALF-EUROPEAN, HALF-ASIAN YOUNG WOMAN ON A PLANT-HUNTING TRIP IN REMOTE CHINA. Her father (a French missionary?) extracts a promise from Caspar to care for the girl and take her back to England if he dies. Some sort of fighting or revolution is happening and the father does die, so Caspar takes her back to England. They marry and the marriage is one of convenience for quite awhile. Caspar continues his life in London which includes his mistress, and the young woman, who is very innocent, lives at his country estate, learns the customs and matures.Caspar realizes it's time for her to be presented, but also realizes that he has to make this a real marriage or else her beauty will attract men who want to seduce her. The consummation takes place outside at his country seat during a picnic, and after she has a nap in the sun, Caspar being aware that the sun is very relaxing. His new wife must learn how to navigate in London society and become a full partner to Caspar, which she does. Caspar is a cool sort of character and not very romantic until he fell in love with her later on in their marriage. But both of them are quite appealing. This author didn't use a lot of emotional drama between her characters. This is the only historical romance about plant-hunting I've seen and I would love to reconnect with it. Thanks in advance!