def build_tree_from_alignment(aln, moltype=DNA, best_tree=False, params={}):
    """Returns a tree from Alignment object aln.

    aln: an xxx.Alignment object, or data that can be used to build one.

    moltype: cogent.core.moltype.MolType object

    best_tree: best_tree suppport is currently not implemented

    params: dict of parameters to pass in to the RAxML app controller.

    The result will be an xxx.Alignment object, or None if tree fails.
    """
    if best_tree:
        raise NotImplementedError

    if '-m' not in params:
        if moltype == DNA or moltype == RNA:
            #params["-m"] = 'GTRMIX'
            # in version 7.2.3, GTRMIX is no longer supported but says GTRCAT
            # behaves like GTRMIX (http://www.phylo.org/tools/raxmlhpc2.html)
            params["-m"] = 'GTRGAMMA'
        elif moltype == PROTEIN:
            params["-m"] = 'PROTGAMMAmatrixName'
        else:
            raise ValueError, "Moltype must be either DNA, RNA, or PROTEIN"

    if not hasattr(aln, 'toPhylip'):
        aln = Alignment(aln)
    seqs, align_map = aln.toPhylip()

    # generate temp filename for output
    params["-w"] = "/tmp/"
    params["-n"] = get_tmp_filename().split("/")[-1]
    params["-k"] = True
    params["-p"] = randint(1,100000)
    params["-x"] = randint(1,100000)

    ih = '_input_as_multiline_string'

    raxml_app = Raxml(params=params,
                      InputHandler=ih,
                      WorkingDir=None,
                      SuppressStderr=True,
                      SuppressStdout=True)

    raxml_result = raxml_app(seqs)

    tree = DndParser(raxml_result['Bootstrap'], constructor=PhyloNode)

    for node in tree.tips():
        node.Name = align_map[node.Name]

    raxml_result.cleanUp()

    return tree