Poplar and willow identification is often difficult, even with experience, mainly because many of those commonly cultivated are cultivars and clones, often of interspecific hybrids. They may even share the same parents and differ only slightly in appearance.
This key is a web app or e-guide that can be used online or offline. To use it offline you will need to follow the instructions carefully and check that it works offline before you leave your network connection.
To use the app offline you must follow the steps:
a) Access the app via the link.
b) Use the Add to Home Screen facility after you have clicked on the App link (not this page!) - this only works on some mobile browsers: on iOS use Safari, and on Android use Chrome, OR
c) Bookmark the page
d) Make sure you access the app via the home screen button or bookmark while you are online. Click around to ensure everything is working and give time (a few minutes) for all the pages to download to your device in the background, THEN
e) Turn off mobile data and wifi to make sure you are offline, close and reopen your browser app or home screen app, and access it again.
If that works while you are offline you should be good to go. Note that if you clear your browser cache the data may be deleted depending on your settings, so you will need to repeat while you are online.
Note: If the process has not worked for any reason, delete the icon on your device, and repeat the process. If you don't delete the icon you may end up with more than one.