| Zannichellia polycarpa | IE, VCH38,VCH39, Belfast | Samuel Alexander Stewart | William Hadden Beeby | 23/8/1876 | 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,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 |
| Zannichellia palustris | IE, VCH38,VCH39, Belfast | Samuel Alexander Stewart | Augustin Ley | 23/8/1876 | BIRM |
| Zannichellia palustris | IE, VCH39 Co. Antrim, Belfast | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Samuel Alexander Stewart | 12/8/1878 | ABS |
| Viola tricolor subsp. curtisii | IE, VCH39 Co. Antrim, Antrim | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles William Hadden Beeby John Gilbert Baker | 25/6/1886 | SLBI |
| Viola tricolor subsp. curtisii | IE, VCH39 Co. Antrim, Lough Neagh | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Augustin Ley | 25/6/1886 | BIRM |
+ | Viola tricolor | IE, VCH39 Co. Antrim, Lough Neagh | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles | 25/6/1886 | MANCH |
| Viola persicifolia | IE, VCH9 Co. Clare, Gort | Samuel Alexander Stewart | William Hadden Beeby | 22/5/1891 | SLBI |
| Viola | IE, VCH9 Co. Clare, Gort | Samuel Alexander Stewart | Augustin Ley | 22/5/1891 | BIRM |
| Valerianella carinata | IE, VCH38 Co. Down, Dundonald | Samuel Alexander Stewart | Augustin Ley | 19/6/1877 | BIRM |
| Utricularia minor | IE, VCH16 West Galway, Roundstone | Samuel Alexander Stewart | William Hadden Beeby | | SLBI |
+ | Stratiotes aloides | IE, VCH39 Co. Antrim, Belfast,Springfield | Samuel Alexander Stewart | Richmond Museum Charles Bailey James Ward | 3/7/1865 | MANCH |
| Spergularia rupicola | IE, VCH38,VCH39, Belfast | Samuel Alexander Stewart | George Stephen West | 8/1869 | BIRM |
| Sesleria caerulea | IE, Galway, Galway Bay | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Augustin Ley | 5/1891 | BIRM |
| Scrophularia auriculata | IE, VCH39 Co. Antrim, Four Mile Burn | Samuel Alexander Stewart | Alexander Somerville | 22/7/1883 | E |
| Saxifraga umbrosa x spathularis = S. x urbium | IE, VCH16 West Galway, Connemara | Samuel Alexander Stewart | Charles Bailey | 10/5/1876 | MANCH |
| Saxifraga umbrosa x hirsuta = S. x geum | IE, VCH1 South Kerry, Brandon Mountain | Samuel Alexander Stewart | Arthur Bennett | 18/7/1878 | SLBI |
| Saxifraga umbrosa | IE, VCH16 West Galway, Ben Lettery | Samuel Alexander Stewart | William Hadden Beeby Arthur Bennett | 10/5/1876 | SLBI |
| Saxifraga umbrosa var. punctata | IE, VCH16 West Galway, Connemara | Samuel Alexander Stewart | Augustin Ley | 10/5/1876 | BIRM |
| Saxifraga hirsuta | IE, Kerry, Cromaglan Mountain | Samuel Alexander Stewart | Samuel Alexander Stewart William Hunt Painter | 18/6/1885 | ABS |
| Salix viminalis x caprea = S. x smithiana | IE, VCH39 Co. Antrim, Kilroot | Samuel Alexander Stewart | George Stephen West | 5/1868 | BIRM |
| Sagina maritima | IE, VCH2 North Kerry, Ballybunnion | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Charles Cardale Babington | 25/7/1885 | ABS |
| Sagina maritima | IE, VCH2 North Kerry, Ballybunnion | Samuel Alexander Stewart | Botanical Exchange Club of The British Isles Augustin Ley | 25/7/1885 | BIRM |
| 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 |
| Primula vulgaris x veris = P. x polyantha | IE, VCH16,VCH17, Salt Hill | Samuel Alexander Stewart | | 14/5/1891 | MANCH |
| Potentilla anglica | IE, VCH39 Co. Antrim, Belfast | Samuel Alexander Stewart | | 7/1893 | 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 |
+ | 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 |