| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | | 10/8/1894 | SLBI |
| 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 obtusifolius | IE, VCH38 Co. Down, Comber | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 27/7/1884 | 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 coloratus | IE, VCH28 Co. Sligo, Coolgagh Loch | Samuel Alexander Stewart | Alfred Fryer Charles Bailey | 4/8/1883 | MANCH |
| Potamogeton berchtoldii | IE, VCH39 Co. Antrim, Lough Neagh | Samuel Alexander Stewart | Alfred Fryer | 28/6/1880 | MANCH |
| 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 |
| 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 |
| 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 |
| 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 |
| Pilosella lactucella | IE, VCH39 Co. Antrim, Cave Hill | Samuel Alexander Stewart | | 5/7/1902 | ABS |
+ | Orobanche purpurea | GB, VC10 Isle of Wight, Totland,Lacy's Farm | Samuel Alexander Stewart | Charles Bailey | 7/1888 | MANCH |
| Orobanche alba | IE, VCH39 Co. Antrim, Cave Hill, Belfast | Samuel Alexander Stewart | Augustin Ley | 8/7/1871 | BIRM |
| 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 |
| Mertensia maritima | IE, VCH38 Co. Down, Glassdrummond | Samuel Alexander Stewart | | 23/6/1889 | SLBI |
| Mentha arvensis x aquatica = M. x verticillata | IE, VCH38 Co. Down, Saul | Samuel Alexander Stewart | | 8/1897 | DBN |
| Mentha aquatica x spicata = M. x piperita | IE, VCH39 Co. Antrim, Carnmoney | Samuel Alexander Stewart | Science & Art Museum Dublin | 14/9/1872 | DBN |
| Mentha aquatica x spicata = M. x piperita | IE, VCH39 Co. Antrim, Carnmoney | Samuel Alexander Stewart | Science & Art Museum Dublin | 12/8/1893 | DBN |
| Mentha aquatica x spicata = M. x piperita | IE, VCH39 Co. Antrim, Masserine Park | Samuel Alexander Stewart | | 2/8/1885 | DBN |
| Melampyrum sylvaticum | IE, VCH38,VCH39, Belfast | Samuel Alexander Stewart | Augustin Ley | 12/6/1872 | BIRM |
| Lobelia dortmanna | IE, VCH38 Co. Down, Mourne Mountains | Samuel Alexander Stewart | Richmond Museum Charles Bailey James Ward | 7/9/1865 | MANCH |
| Lavatera arborea | IE, VCH38 Co. Down, Groomsport | Samuel Alexander Stewart | William Hadden Beeby | 15/7/1871 | SLBI |
+ | Hymenophyllum wilsonii | IE, VCH16 West Galway, Twelve Pins,Bengower | Samuel Alexander Stewart | Charles Bailey | 10/5/1876 | MANCH |
| Hieracium stewartii | IE, VCH38 Co. Down, Hilltown | Samuel Alexander Stewart | | 23/7/1891 | ABS |
| Hieracium orcadense | IE, VCH39 Co. Antrim, Cave Hill, Belfast | Samuel Alexander Stewart | | 21/6/1896 | ABS |
| Hieracium latobrigorum | IE, VCH39 Co. Antrim, Cranfield | Samuel Alexander Stewart | | 27/7/1890 | SLBI |
| Hieracium latobrigorum | IE, VCH39 Co. Antrim, Cranfield | Samuel Alexander Stewart | | 27/7/1899 | ABS |
| Hieracium gothicoides | IE, VCH38 Co. Down, Hilltown | Samuel Alexander Stewart | | 24/7/1891 | ABS |
| Hieracium friesii | IE, VCH38 Co. Down, Hilltown | Samuel Alexander Stewart | William Hadden Beeby | 24/7/1891 | SLBI |
| Hieracium basalticola | IE, VCH39 Co. Antrim, Knockagh | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles | | ABS |