| Salix viminalis x caprea = S. x smithiana | IE, VCH39 Co. Antrim, Kilroot | Samuel Alexander Stewart | George Stephen West | 5/1868 | BIRM |
| Spergularia rupicola | IE, VCH38,VCH39, Belfast | Samuel Alexander Stewart | George Stephen West | 8/1869 | BIRM |
| Zannichellia polycarpa | IE, VCH38,VCH39, Belfast | Coslett Herbert Waddell Samuel Alexander Stewart | Allan Octavian Hume Coslett Herbert Waddell | 7/1904 | SLBI |
| Zannichellia polycarpa | IE, VCH38,VCH39, Belfast | Coslett Herbert Waddell Samuel Alexander Stewart | Allan Octavian Hume Coslett Herbert Waddell | 7/1904 | SLBI |
| Zannichellia polycarpa | IE, VCH38 Co. Down, Belfast | Coslett Herbert Waddell Samuel Alexander Stewart | Allan Octavian Hume Coslett Herbert Waddell | 7/1904 | SLBI |
| Hieracium basalticola | IE, VCH39 Co. Antrim, Sallagh Braes | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Frederick Townsend | 15/6/1890 | SLBI |
| Callitriche hamulata | IE, VCH38 Co. Down, Castlewellan Forest Park | Samuel Alexander Stewart | Watson Botanical Exchange Club Coslett Herbert Waddell Harold Stuart Thompson | 7/6/1897 | BIRM |
| Equisetum hyemale x variegatum = E. x trachyodon | IE, VCH39 Co. Antrim, Belfast,Colin Glen | Samuel Alexander Stewart | Harold Stuart Thompson | 22/6/1879 | BIRM |
| Najas flexilis | IE, VCH16 West Galway, Roundstone | Samuel Alexander Stewart | Harold Stuart Thompson | 15/8/1877 | BIRM |
| Apium inundatum | IE, VCH38 Co. Down, Downpatrick | Samuel Alexander Stewart | | 16/9/1886 | SLBI |
| Apium nodiflorum x inundatum = A. x moorei | IE, VCH16 West Galway, Doonpatrick | Samuel Alexander Stewart | Samuel Alexander Stewart | 7/1880 | BIRM |
| Arctostaphylos uva-ursi | IE, VCH9 Co. Clare, Black Head | Samuel Alexander Stewart | Robert Large Baker | 5/1876 | BIRM |
| Arenaria ciliata | IE, VCH28 Co. Sligo, Kings Mountain | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Allan Octavian Hume | 18/7/1879 | SLBI |
| Carex dioica | IE, VCH39 Co. Antrim, Divis Hill | Samuel Alexander Stewart | | 12/5/1866 | BM |
| Carex distans | IE, VCH39 Co. Antrim, Black Head | Samuel Alexander Stewart | | 29/6/1872 | BON |
| Carex remota | IE, VCH39 Co. Antrim, Cushendall | Samuel Alexander Stewart | | 28/6/1866 | BM |
| Daboecia cantabrica | IE, Mayo, Uggool | Samuel Alexander Stewart | Robert Large Baker | 19/8/1877 | BIRM |
| Dryas octopetala | IE, VCH9 Co. Clare, Black Head | Samuel Alexander Stewart | | 12/5/1876 | SLBI |
| Dryas octopetala | IE, VCH28 Co. Sligo, Benbulben | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles | 16/7/1879 | SLBI |
+ | Equisetum hyemale x variegatum = E. x trachyodon | IE, VCH39 Co. Antrim, Colin Glen | Samuel Alexander Stewart | | 22/6/1879 | BIRM |
| Equisetum hyemale x variegatum = E. x trachyodon | IE, VCH39 Co. Antrim, Colin Glen | Samuel Alexander Stewart | | 1/7/1872 | BON |
| Eriocaulon aquaticum | IE, VCH16 West Galway, Roundstone | Samuel Alexander Stewart | | 29/7/1867 | BON |
| Euphorbia hyberna | IE, Kerry, Cromaglan Mountain | Samuel Alexander Stewart | | 18/6/1885 | ABS |
| Euphorbia hyberna | IE, Kerry, Cromaglan Mountain | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles | 15/6/1885 | ABS |
| Hieracium basalticola | IE, VCH39 Co. Antrim, Knockagh | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles | | ABS |
+ | Hieracium basalticola | IE, VCH39 Co. Antrim, Sallagh Braes | Samuel Alexander Stewart | | 15/6/1890 | BIRM |
| Hieracium gothicoides | IE, VCH38 Co. Down, Hilltown | Samuel Alexander Stewart | | 24/7/1891 | ABS |
| Hieracium latobrigorum | IE, VCH39 Co. Antrim, Cranfield | Samuel Alexander Stewart | | 27/7/1899 | ABS |
| Hieracium latobrigorum | IE, VCH39 Co. Antrim, Cranfield | Samuel Alexander Stewart | | 27/7/1890 | SLBI |
| 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 |
| Mentha arvensis x aquatica = M. x verticillata | IE, VCH38 Co. Down, Saul | Samuel Alexander Stewart | | 8/1897 | DBN |
| Mertensia maritima | IE, VCH38 Co. Down, Glassdrummond | Samuel Alexander Stewart | | 23/6/1889 | SLBI |
| Pilosella lactucella | IE, VCH39 Co. Antrim, Cave Hill | Samuel Alexander Stewart | | 5/7/1902 | ABS |
+ | 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 | | 10/8/1894 | ABS |
| Potamogeton perfoliatus x crispus = P. x cooperi | IE, VCH39 Co. Antrim, Templepatrick | Samuel Alexander Stewart | | 10/8/1894 | SLBI |
| Potentilla anglica | IE, VCH39 Co. Antrim, Belfast | Samuel Alexander Stewart | | 7/1893 | SLBI |
| Rosa spinosissima x canina = R. x hibernica | IE, VCH39 Co. Antrim, Belfast | Samuel Alexander Stewart | | 12/7/1875 | SLBI |