import re


def parse_rst_params(doc):
    """
    Parse a reStructuredText docstring and return a dictionary
    with parameter names and descriptions. 
    
    >>> doc = '''
    ... :param foo: foo parameter
    ...     foo parameter
    ... 
    ...  :param bar: bar parameter
    ...  :param baz: baz parameter
    ...         baz parameter
    ...     baz parameter
    ...  Some text.
    ... '''
    >>> params = parse_rst_params(doc)
    >>> params['foo']
    'foo parameter foo parameter'
    >>> params['bar']
    'bar parameter'
    >>> params['baz']
    'baz parameter baz parameter baz parameter'
    """
    param_re = re.compile(r"""^([ \t]*):param\ 
                              (?P<param>\w+):\ 
                              (?P<body>.*\n(\1[ \t]+\w.*\n)*)""",
                          re.MULTILINE|re.VERBOSE)
    params = {}
    for match in param_re.finditer(doc):
        parts = match.groupdict()
        body_lines = parts['body'].strip().split('\n')
        params[parts['param']] = ' '.join(s.strip() for s in body_lines)
    
    return params