Syringa is the scientific name for lilac. (See my entry on Lilac for description and history). I can find no consistent distinction between lilac and syringa as plants. It is sometimes asserted that syringa is the more generic name, as if lilacs are one of several types of syringa, but I have not found any species of syringa that is not also labeled lilac (Hogan 1387). In E.T. Ellis’s encyclopedic 1930 guide, The Garden for Expert and Amateur, syringa does not have its own entry and varieties are listed in shrubs as “LILAC” (980). Vita Sackville-West offers a possible dis-ambiguation when she remarks in a 1948 gardening column that lilac is now called syringa by “the experts” and “what we used to call syringa is now called philadelphus” (Garden Book 73). Philadelphus coronaries, also known as “sweet mock orange,” or “English dogwood” is a shrub in the hydrangea family growing up to ten feet tall, bearing fragrant, white “bowl-shaped flowers” in the early summer.
I get the sense that Woolf tends to follow the old fashioned nomenclature and uses “syringa” to refer to what we would now call “mock orange.” She does not seem to think that syringa and lilac are the same plant as she employs “syringa” to refer to bushes rather than trees -- syringa isn’t persistently paired with laburnum trees and doesn’t droop as lilac does -- and there is less reference to its color, which is never specified as purple. The one problem with this explanation is that Woolf does once refer to “mock orange” being in bloom at Monk’s House at the end of May 1920 (D4 43), which suggests that she didn’t recognize “syringa” as being the same thing as mock orange either.
Literary or symbolic allusions to syringa and mock orange are rare before the modern era. Although, in poetic allusions aligned with Whitman’s pastoral elegy for Lincoln, lilac is traditionally a flower of mourning, in her Victorian codex for the language of flowers Kate Greenaway associates lilac with humility, the first emotions of love, and youthful innocence (27), while it is syringa that is allied to memory (39). However, although syringas are associated with memory, they are not necessarily emblems of mourning. To make things even more confusing, Greenaway lists mock orange as signifying “Counterfeit” (29).
Woolf mentions syringa five times, in two clusters. They first appear in 1925 near the end of Mrs. Dalloway in a list of semi-exotic plants successfully bred in the suburban Manchester gardens of Sally Rosseter (nee Seaton), Clarissa’s youthful inamorata, now married and happily bourgeoisie in her wealth: “hydrangeas, syringas, very, very rare hibiscus lilies that never grow north of the Suez Canal” (MD 186). A few years later the shrubs are again mentioned in a slightly homo-erotic context when Woolf writes to her beloved Vita Sackville-West referring (in a pun on her writing materials) to the double bed sheets at Long Barn, the country-cottage precursor to Sissinghurst castle: “fit for Long Barn on a summer’s night a June night with Ethel Smyths nightingales whistling in the syringas by the swimming pool” (L3 569).
A second cluster of syringas surfaces in the late thirties, here more frequently and conventionally associated with the idea of memory. In the 1917 chapter of The Years while the characters dine in the cellar due to air raids overhead, reciting fragments of poetry from Robert Burns, Shelley, and Sir Walter Scott, Eleanor and Sara and Maggie reminisce about waltzing in the bedroom as young girls to a tune with the words “All men loved me when I was young…. Roses and syringas hung, when I was young, when I was young” (TY 272), a reference aligned not only to syringa’s conventional association with memory but also with lilac’s traditional evocation of the youthful innocence of first love.
Another memory of syringas emerges the year that Woolf’s family history novel was published, in her 1937 review of My Sporting Life by John Waller Hills, aka “Jack” Hills,” the friend of Woolf’s mother Julia and persistent suitor of her half-sister Stella, whom he married after Julia’s death. When Stella died soon after -- from “peritonitis complicated by pregnancy” (Hussey, A to Z 111) -- Jack became quite close to Virginia, and especially to her sister Vanessa. As Hussey recounts, Hills discussed Plato with the young Virginia, was frankly informative about sexual issues, taught the young Stephen children how to hunt moths and encouraged their collecting, and thus was an essential figure in her childhood and adolescence (112). Her sustained affection for him is shown in her review, not published until after her death, in which she praises the sensory immersion prompted by his descriptive writing. One of the passages she quotes as an example in which the reader “sees the scene though the words” (E6 495) contains a vivid reference to syringa, switching the memory of the flower from a feminine to a masculine context: “The flowering trees had long since lost their blossoms, but on coming to a syringa bush I walked suddenly into its scent, and was drenched as in a bath. I sat on the path. I stretched my legs. I lay down, finding a tuft of grass for pillow, and the yielding sand for mattress. I fell asleep” (E6 494). Interestingly, in her memoir, “A Sketch of the Past,” Woolf also associates Jack Hills with roses, describing the rapturous vision of the love between Jack and Stella as reminding her of the Burn’s poem, “My love is like a red red rose” (MOB 105)
Memorialized in her diary a year later, Woolf’s last syringa evokes another masculine figure from Woolf’s childhood, Sir Walter Scott, whose novels were favorites of her father (and Mr Ramsay in To the Lighthouse). In June of 1938, on a motor trip with Leonard through northern England and Scotland, she recorded stopping at Dryburgh in Berwickshire to visit Scott’s grave: “the Abbey is impressive and the river running at the bottom of the field. And all the old Scots ruins standing round him. I picked a white syringa in memory but lost it. An airy place but Scott is much pressed together” (D5 152). Whether Woolf’s syringa is a white lilac or a mock orange, with or without roses, it conjures a number of memories, much pressed together.
 Folkard notes that John Evelyn (about whom Woolf wrote) “applied the name Syringa to the lilac” (284). See also the Wikipedia entry https://en.wikipedia.org/wiki/Syringa Accessed 4/20/2022. The Portland [Oregon] Nursery also has information on Lilacs which identifies cultivars of Syringa vulgaris as the most common species: https://www.portlandnursery.com/shrubs/syringa Accessed 4/20/2022.
 See Wikipedia on the most common garden variety, Philadephus coronarius in https://en.wikipedia.org/wiki/Philadelphus_coronarius The entry on Philadelphus in general refers to syringa as an “entirely misleading name” for Philadelphus.
https://en.wikipedia.org/wiki/Philadelphus Both accessed April 21, 2022.
 In the Harcourt Annotated Edition, Eleanor McNees identifies the lines about giving “his bridle reins a shake” and saying “Adieu forevermore” as coming from Sir Walter Scott’s “The Rover’s Adieu” (TY 448). David Bradshaw and Ian Blyth provide an alternative citation in the Shakespeare’s Press edition, attributing the lines to the Robert Burns poem “It was a’ for our rightful king” (notes to p. 202 on p. 341). In the Cambridge Edition of The Years, Anna Snaith points out that the line about the moon rising above a dark moor is quoted from Shelley’s “Stanzas -- April 1814” (501). She identifies the syringa waltz as an “unidentified song” based on the 1907 classic “After the ball is over” (502).