▁flower . ▁ ▁Description ▁P ter ost yl is ▁dil at ata ▁is ▁a ▁terrest rial , ▁ ▁per enn ial , ▁decid uous , ▁her b ▁with ▁an ▁under ground ▁t uber ▁and ▁when ▁not ▁flow ering , ▁a ▁ro set te ▁lying ▁flat ▁on ▁the ▁ground . ▁Flow ering ▁plants ▁lack ▁a ▁ro set te ▁but ▁have ▁a ▁single ▁green ▁and ▁white ▁flower ▁on ▁a ▁flow ering ▁stem ▁ ▁tall ▁with ▁three ▁to ▁five ▁stem ▁leaves . ▁The ▁stem ▁leaves ▁are ▁ ▁long ▁and ▁ ▁wide . ▁The ▁flower ▁is ▁green ▁and ▁white , ▁ ▁long , ▁ ▁wide . ▁The ▁d ors al ▁se pal ▁and ▁pet als ▁form ▁a ▁h ood ▁over ▁the ▁column ▁with ▁the ▁pet als ▁fla red ▁and ▁the ▁d ors al ▁se pal ▁having ▁a ▁short ▁point . ▁ ▁The ▁later al ▁sep als ▁are ▁ere ct , ▁f used ▁for ▁most ▁of ▁their ▁length ▁except ▁for ▁their ▁thread - like ▁tips ▁which ▁are ▁ ▁long . ▁The ▁later al ▁sep als ▁are ▁in ▁close ▁contact ▁with ▁the ▁g ales ▁and ▁have ▁a ▁bul ging ▁sin us ▁between ▁them . ▁The ▁lab ell um ▁is ▁about ▁ ▁long , ▁ ▁wide ▁and ▁not ▁visible ▁outside ▁the ▁int act ▁flower . ▁Flow ering ▁occurs ▁from ▁May ▁to ▁August . ▁ ▁Tax onomy ▁and ▁naming ▁P ter ost yl is ▁dil at ata ▁was ▁first ▁formally ▁described ▁in ▁ 1 9 8 4 ▁by ▁Alex ▁George ▁from ▁a ▁spec imen ▁collected ▁near ▁Bl uff ▁Kn oll .