EDIT

        $markerTypesEmpty = array();

  $markerTypesEmpty['markerTypes'] = '';

    $taxonDescriptions = cdm_ws_get(CDM_WS_PORTAL_TAXON_DESCRIPTIONS, $taxon->uuid, queryString($markerTypesEmpty)); //retrieve all description for the taxon

    $nonStructuredDescriptions = array();

    if($taxonDescriptions != null){

      foreach ($taxonDescriptions as $taxonDescription) {

        if($hasStructuredData){

          $structured_description_featuretree_uuid = variable_get(CDM_DATAPORTAL_STRUCTURED_DESCRIPTION_FEATURETREE_UUID, false);

          $naturallanguage_textData = cdm_ws_get(CDM_WS_DESCRIPTION_NATURALLANGUAGE_DESCRIPTION, array($taxonDescription->uuid, $structured_description_featuretree_uuid));

          if(!$naturallanguage_textData){

            drupal_set_message('The \'FeatureTree\' for the generation of natural language representations is not configured correctly, please select a \'FeatureTree\' in the '.l('CDM Dataportal Settings', 'admin/settings/cdm_dataportal/layout/taxon'), 'warning');

          }