| Mertensia maritima | IE, VCH38 Co. Down, Glassdrummond | Samuel Alexander Stewart | | 23/6/1889 | SLBI |
| Najas flexilis | IE, VCH16 West Galway, Roundstone | Samuel Alexander Stewart | William Hadden Beeby Arthur Bennett | 15/8/1887 | SLBI |
| Najas flexilis | IE, VCH16 West Galway, Roundstone | Samuel Alexander Stewart | Augustin Ley | 15/8/1877 | BIRM |
| Najas flexilis | IE, VCH16 West Galway, Roundstone | Samuel Alexander Stewart | Harold Stuart Thompson | 15/8/1877 | BIRM |
| Orobanche alba | IE, VCH39 Co. Antrim, Cave Hill, Belfast | Samuel Alexander Stewart | Augustin Ley | 8/7/1871 | BIRM |
+ | Orobanche purpurea | GB, VC10 Isle of Wight, Totland,Lacy's Farm | Samuel Alexander Stewart | Charles Bailey | 7/1888 | MANCH |
| Pilosella lactucella | IE, VCH39 Co. Antrim, Cave Hill | Samuel Alexander Stewart | | 5/7/1902 | ABS |
| Pilosella peleteriana | IE, VCH39 Co. Antrim, Core Hill, Belfast Cultivated | Coslett Herbert Waddell | Botanical Exchange Club of The British Isles Coslett Herbert Waddell Edward Francis Linton Samuel Alexander Stewart | 8/1900 | ABS |
| Pinguicula grandiflora | IE, VCH1 South Kerry, Mangerton | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Augustin Ley | 25/6/1885 | BIRM |
| Pinguicula grandiflora | IE, Kerry, Mangerton | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles William Hadden Beeby | 22/6/1885 | SLBI |
| Polygala vulgaris | IE, VCH28 Co. Sligo, Benbulben | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Augustin Ley | 16/7/1879 | BIRM |
| Polygala vulgaris | IE, VCH28 Co. Sligo, Benbulben | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Edward Francis Linton | 16/7/1879 | SLBI |
| Polygala vulgaris | IE, VCH28 Co. Sligo, Benbulben | Samuel Alexander Stewart | Reginald Wiliam Scully | 3/8/1883 | SLBI |
| Potamogeton alpinus | IE, VCH38 Co. Down, Newcastle | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 8/8/1890 | MANCH |
| Potamogeton alpinus | IE, VCH39 Co. Antrim, Belfast | Samuel Alexander Stewart | Richmond Museum Charles Bailey James Ward | 2/7/1866 | MANCH |
| Potamogeton alpinus | IE, VCH39 Co. Antrim, Lough Mourne | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | | MANCH |
| Potamogeton berchtoldii | IE, VCH39 Co. Antrim, Lough Neagh | Samuel Alexander Stewart | Alfred Fryer | 28/6/1880 | MANCH |
| Potamogeton coloratus | IE, VCH28 Co. Sligo, Coolgagh Loch | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 4/8/1883 | MANCH |
| Potamogeton lucens x gramineus = P. x angustifolius | IE, VCH30 Co. Cavan | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Arthur Bennett | 6/7/1881 | ABS |
| Potamogeton lucens x gramineus = P. x angustifolius | IE, VCH38 Co. Down, Lagan | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 12/8/1894 | MANCH |
| Potamogeton lucens x gramineus = P. x angustifolius | IE, VCH40 Co. Londonderry, coleraine | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Charles Bailey | 29/7/1883 | MANCH |
| Potamogeton obtusifolius | IE, VCH38 Co. Down, Comber | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 27/7/1884 | MANCH |
| Potamogeton perfoliatus | IE, VCH39 Co. Antrim, Bushmills | Samuel Alexander Stewart | Richmond Museum Charles Bailey | 7/1866 | MANCH |
| Potamogeton perfoliatus | IE, VCH39 Co. Antrim, Lough Mourne | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 19/7/1880 | MANCH |
+ | Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Sixmile River above Templepatrick | Samuel Alexander Stewart | | 10/8/1894 | BIRM |
| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 8/1894 | MANCH |
| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | Charles Bailey Samuel Alexander Stewart | 10/8/1894 | MANCH |
| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 10/8/1894 | MANCH |
| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | Manchester Museum Charles Bailey | 10/8/1894 | MANCH |
| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Augustin Ley | 10/8/1894 | BIRM |
| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | | 10/8/1894 | ABS |
| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | | 10/8/1894 | SLBI |
+ | Potamogeton praelongus | IE, VCH39 Co. Antrim, Belfast,Lagan Canal | Samuel Alexander Stewart | Charles Bailey James Ward | 2/7/1866 | MANCH |
+ | Potamogeton praelongus | IE, VCH39 Co. Antrim, Belfast,Lagan Canal | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 23/6/1873 | MANCH |
+ | Potamogeton praelongus | IE, VCH39 Co. Antrim, Rathlin Island,Ushet Lough | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 4/8/1882 | MANCH |
| Potamogeton praelongus | IE, VCH39 Co. Antrim, Sixmile River | Samuel Alexander Stewart | Arthur Bennett | 8/1894 | SLBI |
| Potentilla anglica | IE, VCH39 Co. Antrim, Belfast | Samuel Alexander Stewart | | 7/1893 | SLBI |
| Primula vulgaris x veris = P. x polyantha | IE, VCH16,VCH17, Salt Hill | Samuel Alexander Stewart | | 14/5/1891 | MANCH |
| Rosa spinosissima x canina = R. x hibernica | IE, VCH38 Co. Down, Holywood | Samuel Alexander Stewart | Frederick Arnold Lees | 6/1871 | SLBI |
| Rosa spinosissima x canina = R. x hibernica | IE, VCH39 Co. Antrim, Belfast | Samuel Alexander Stewart | | 12/7/1875 | SLBI |