TreeView control in C#

Sure, here it is:

The submit button code:

protected void btSubmit_Click(object sender, EventArgs e)
{
    TraverseTreeView(tvTaxon); //should return all nodes that were checked by user
}

The pertinent 'Traverse' code snippet:

private void TraverseTreeView(TreeView tview)
{
    //Create a TreeNode to hold the Parent Node
    TreeNode temp = new TreeNode();
    string taxon;
    //Loop through the Parent Nodes
    for (int k = 0; k < tview.Nodes.Count; k++)
    {
        //Store the Parent Node in temp
        temp = tview.Nodes[k];
        //Display the Text of the Parent Node i.e. temp
        if (temp.Checked) //PROBLEM HERE! This will always evaluate to 
                          //false, no matter if user checks node or not
        {
            //store in session variable;
        }
    }
    //Now Loop through each of the child nodes in this parent node i.e.temp
    for (int i = 0; i < temp.ChildNodes.Count; i++)
        visitChildNodes(temp.ChildNodes[i]); //send every child to the function for further traversal
}

Check viewstate of your page is it false?

2nd are you binding your treeview everytime when page is loading or Init? ideally if viewstate is true of your page you shouldn't bind data to treeview every time. Bind it on first page load i.e.

if(!IsPostBack)
   tvTaxon.DataSource = DataSource...

FYI:
There are three basic phases of every server control happens every time:
Init
Load
Render

if there is any data control TreeView in your case then databind also happens. Most of the data control adds datasource to viewstate when first time you supply data to it, on subsequent postbacks TreeView extracts data from viewstate thats why we don't need to pass it again-n-again.

If you are sure you are not binding your TreeView everytime time please add the code where you are binding your treeview to the SQL datasource. the code should include the event name in which you are assigning the source for example Page_load, the code should also show if there is any if statment prior to assigning datasource.

ideally you should add all code i.e. markup of aspx + code where you are binding data + code where you are evaluating check statements like you added in the first comment.

Thanks,
Hemant