-ia: ending of Greek and Latin nouns denoting quality of or state of being.

Iber'is: from the Greek iberis,a name used by Dioscorides, indicating a plant from Iberia, the ancient Latin name of the large southwestern peninsula of Europe, from Greek Iberes, the name of a Celtic people of ancient Spain. The genus Iberis was published by Carl Linnaeus in 1753.

idae'us: Stearn says of Mt. Ida, Crete, less often Asia Minor. Another source with specific reference to Rubus idaeus says "idaeus comes from Mount Ida, near Troy, in the North East of Turkey, which according to what Dioscorides reports was particularly rich in this species." In Greek mythology, Idaeus was the son of Dares Phrygius and the charioteer of Priam during the Trojan War.

I'lex: holly, from the Latin name of the holm-oak, Quercus ilix, possibly borrowed from some non-Indo-European language. The genus Ilex has been variously called holly, winterberry and gallberry, and was published by Carl Linnaeus in 1753.

Iliam'na: the Jepson Manual says "Greek: derivation uncertain." David Hollombe unearthed an article by Weber and Fryxell in Sida, Contributions to Botany (2002) that suggests that Edward Lee Greene had heard of the Iliamna volcano, glacier and/or lake in Alaska and just liked the sound of the name. The genus Iliamna was published by Greene in 1908 and is called globe-mallow.

ilicifo'lia: with foliage being similar to that of the genus Ilex.

illinoen'sis/illinoinen'sis: of or from Illinois.

ilven'sis: Latinized form of the name of the isle of Elba, Italy, where Napoleon was exiled.

imbricar'ia: pertaining to wooden roof tiles or shingles, from imbrex, “roof tile.” The Latin suffix –arius often meant “a person working or engaged in.” In the case of Quercus imbricaria, it comes from the common name in English, “shingle oak”, applied because the wood was used to make shingles.

imbrica'ta: "overlapping, closely put together," referring to the calyx lobes which are imbricate laterally in fruit. Derives from the Latin word imbricatus which means "overlapping like shingles."

Impa'tiens/impatiens: from the Latin impatiens, "desiring immediate action," and impatientem, so called in reference to the valves of the seed pods, which discharge forcibly at a slight touch.and referring to the sudden dehiscence of the capsules. The genus Impatiens was published by Carl Linnaeus in 1753 and is variously called jewelweed, touch-me-not, and snapweed. Other genera like Cardamine have impatiens as a specific epithet.

Impera'ta: named for the Neopolitan apothecary or pharmacist Ferrante Imperato (1550-1625) who had one of the earliest collections of natural history specimens in Italy (possibly in Europe) and was the author of Historia Naturale (first published in 1599) which was a catalog of his 'Museum' specimens containing animals, shells, birds, sea creatures, fossils, clays, metallic ores, marble and gems. He travelled extensively for the purpose of collecting and corresponded with other contemporary naturalists. The genus Imperata was published by Domenico Maria Leone Cirillo in 1792.

in-: without.

inca'na/inca'num: grayish or hoary.

incarna'ta/incarna'tum/: flesh-colored.

incer'tus: doubtful, uncertain, and so named largely as a result of lingering confusion with Cenchrus spinifex.

inci'sa: incised, deeply or irregularly cut.

incogna'ta: untried, unrecognized, unknown, from the Latin cognoscere, "to be known, be acquainted with," and the negative prefix in-.

incomple'ta: lacking parts.

incomp'ta: unadorned.

incur'va: bent inward.

indecor'a: from the Latin in-, "not" and decorus, "beautiful," thus unattractive, unornamented, without decoration. It's curious that the species Packera indecora is called elegant ragwort. There are over 50 taxa that use this specific epithet.

in'dica/in'dicum/in'dicus: of or from or referring in some way to India.

iner'mis: unarmed, defenceless, without prickles or thorns, from in-, "without," and arma, "defensive arms."

infir'ma: weak, feeble, trivial, from the Latin in-, "without," and firmus, "steadfast, strong."

infla'ta: inflated, in reference to some floral  part such as the stem.

inflex'a/inflex'us: bent inwards.

innomina'ta: unnamed, nameless, without a name.

inodor'us: without a scent or odor.

inox'ia: without prickles, harmless (often spelled innoxia), the epithet referring to the spines not being harmful, noxi/us/a/um being a Latin adjective meaning "harmful" and in- being a Latin prefix that effectively translates to “not.” The International Plant Names Index lists both Datura inoxia and Datura innoxia as having been published by Philip Miller in 1768. Several other taxa are listed with innoxia as the specific epithet. An interesting article by Mary Barkworth and Sami Rabei in Taxon 12 March 2020 entitled "Proposal to Conserve the Name Daturs innoxia (Solanaceae) with that Spelling" gives an etymological history of the epithet, how it has been used by various botanists and taxonomists, and how often references have been made to one or the other spelled names, and finding that innoxia has been used more than inoxia, on that basis alone recommends the former name.However, Miller's publication of the name was inoxia, and I see no valid reason to change it.

insitit'ia: Both Stearn and Gledhill include this name as meaning grafted. The following is quoted from an article entitled "What is Prunus insititia?" by F.A. Waugh in the Botanical Gazette, Vol 27, No. 6, published in 1899 by the University of Chicago Press: "This species seems to have been a puzzle since Linnaeus published it. It has been a stumbling block to all American botanists who have not been able gracefully to avoid it. It seems to me that it is time to lay this species name to its final rest, and the following remarks are offered in the hope of contributing to that result. The term insititia has been translated as grafted, and it has been said that Linnaeus meant to characterize under this name the grafted garden plums as distinct from the seedling forms of Prunus domestica which he knew; but Karl Koch (in his Dendrologie, 1869) gives a different and more plausible interpretation. He says "the word insititia means here exotic, in distinction from the Sloe [Prunus spinosa] which Linnaeus had seen wild in Sweden. Unfortunately we are obliged to depend largely on outside evidence for our knowledge of what Linnaeus meant to include in his Prunus insititia, the only direct testimony being the original description cited herewith." He goes on to list the various botanists with the different names attributed to this purported species, and gives considerable evidence based on personal examination that all of those specimens labeled as such in the National Herbarium, the Torrey Herbarium at Columbia, and the herbarium of the Missouri Botanical Garden are actually Prunus spinosa or Prunus domestica, and Waugh concludes by saying that "The study of these specimens, taken with the literature of the subject, points clearly to the conclusion that there is no such species as Prunus insititia." This being said, that was one man's opinion in 1899 and it may or may not have been shown more recently to have been shortsighted or just wrong. However, the Plant List, a joint venture of Kew Gardens and the Missouri Botanical Garden currently lists the name as either a synonym of Prunus domestica or as unresolved.

integer'rima: with a smooth edge, undivided.

integrifo'lia/integrifo'lium: indicates that the leaf margins are entire, uncut, not toothed.

intercur'sum: Gledhill says: "intervening, crossing over," from Latin intercurso, but Wiktionary says that intercursus means "mingled with." Jaeger's Source-book has the root inter as meaning "between, among," and cursio, as "a running," and a website of the Morton Arboretum in Chicago defines intercursum as "running between." I could find nothing that explains the appluication of this name to the species Linum intercursum, and its common name, sand plain flax, is no help.

interme'dia: intermediate, indicating an observation that a species was probably considered as being halfway or partway between two others with regard to some particular characteristic, e.g. tall, short, and "intermediate."

intrica'ta/intrica'tum: intricate, tangled.

in'tybus: derived from Egyptian tybi, "January," the month that this species was customarily eaten.

In'ula: a Latin name for a plant called elecampane which is itself a corruption of the ante-Linnaean name Enula campana, so called from its growing wild in Campania. This was an ancient herb described by both Pliny and Dioscorides. Botanical.com says, "Inula, the Latin classical name for the plant, is considered to be a corruption of the Greek word Helenion which in its Latinized form, Helenium, is also now applied to the same species. There are many fables about the origin of this name. Gerard tells us: 'It took the name Helenium of Helena, wife of Menelaus, who had her hands full of it when Paris stole her away into Phrygia.' Another legend states that it sprang from her tears: another that Helen first used it against venomous bites; a fourth, that it took the name from the island Helena, where the best plants grew." It had many medicinal uses such as among other things for coughs, consumption, asthma and bronchitis. The genus Inula was published by Carl Linnaeus in 1753, and is called elecampane.

inunda'ta: of marshes or places which flood periodically.

involucra'ta: provided with an involucre, a ring of bracts surrounding or enclosing a head of several flowers.

Ionac'tis: from the Greek ion and aktis meaning "violet ray." The genus Ionactis is called stiff-leaved aster and was published by Edward Lee Greene in 1897.

ipecacuan'hae: from Portuguese ipecacuanha, in turn from Tupi ɨpekakwánʸa, from ɨpéka, "duck," and akwánʸa, "penis." Clearly this name has something to do with the emetic ipecac. Gledhill says: "a Tupi vernacular name for the drug used against dysentery from the rhizomes of Cephaelis ipecacuanha," The Tupi people were one of the largest groups of indigenous Brazilians before its colonization, and their name for ipecacuanhae translates as 'road-side sick-making plant.' The species Euphorbia ipecacuanhae is called Carolina or American ipecac, or ipecac spurge.

Ipomoe'a: from the Greek ips, "a worm," and homoios, "like," thus "like a worm," referring to the twining habit of the plant's growth. The genus Ipomoea is called morning glory and was published in 1753 by Carl Linnaeus.

Ipomop'sis:from the Greek ipo, "to strike," and opsis, "appearance," thus of striking appearance? An article written by James Edward Smith (?) in Rees's Cyclopaedia gives the Greek root ipoo for "striking." "Rees's Cyclopaedia, or The New Cyclopaedia, or, Universal Dictionary of the Arts and Sciences was edited by Revd. Abraham Rees (1743-1825). It appeared in parts between January 1802 and August 1820, and ran to 39 volumes of text, 5 volumes of plates, and an atlas. It contains around 39 million words, and more than 500 of the articles are of monograph length. An American edition, with 42 volumes of text and 6 of plates was published by Samuel Bradford of Phildelphia between 1806-1822, with additional American material. It was written by about 100 contributors, most of whom were nonconformists. They were specialists in their fields, covering the arts and humanities, agriculture, science, technology, and medicine. Its engraved plates are particularly fine, being the work of artists like John Farey, Jr., and the engraver Wilson Lowry. At the time of its publication Rees's Cyclopaedia was thought to be subversive, and the editors went out of their way to emphasise their Englishness." (from Wikipedia)  The type of the genus, Ipomopsis rubra, was collected by Mark Catesby and described by Johann Jakob Dillenius in Hortus Elthamensis. Linnaeus named it Polemonium rubrum in his Species Plantarum. It was subsequently renamed Ipomoea rubra in J.A. Murray's update of Linnaeus' Systema Vegetabilium, then renamed again Ipomopsis elegans in Andre Michaux's Flora Boreali-Americana (1803). Carl Ludwig Willdenow published it as Cantua coronopifolia in 1797 and Christiaan Hendrik Persoon had transfered it into Gilia in 1805, so this is what many botanists continued to refer to it as. James Smith in Exotic Botany (1806) says: "About its genus there as been much uncertainty. Linnaeus first made it a Polemonium and then an Ipomoea, but it agrees with neither. The learned Jussieu supposed it might be reduced to his genus of Cantua, and has lately again advanced that opinion; but the want of winged seeds, the membranous calyx, and the totally different habit, abundantly justify Michaux in establishing it as a new genus; and we adopt his name, which seems to express the dazzling brilliance of the flower." Thomas Nuttall in his Genera of North American Plants, renamed it Ipomeria coronopifolia and said: "I have, in restoring this genus of Michaux, altered his name merely for the sake of euphony [meaning an agreeable sound, especially in the phonetic quality of words], but retained the allusion, without venturing to criticize its questionable composition as formed in part from the name of the preceding genus, Ipomoea, with the addition of -opsis as indicative of their common resemblance... That Michaux's name has been independently derived from the Greek, without any reference to Ipomoea, and founded upon its striking appearance, as supposed by the editor of the [above referenced] article in Rees's Encyclopedia, seems altogether improbable." The fern authority and geologist Edgar T. Wherry was the first in 1936 to utilize its current name. Umberto Quattrocchi's Dictionary of Plant Names simply says of the generic epithet Ipomopsis, "resembling Ipomoea." The foregoing is a perfect example of how difficult it is sometimes to say what a specific epithet means, what it refers to, or from where it is derived. Thanks to David Hollombe for most of the references included. The genus Ipomopsis was published by André Michaux in 1803.

iracun'da: wrathful, inclined to anger, from Late Latin iracundus, from ira, "anger, wrath, rage, passion." I have no idea whatsoever how such a name could apply to a plant, but one of the common names of Crataegus iracunda is passionate hawthorne.

Iresi'ne: from Greek eiresione, a wreath or staff entwined with strips of wool, alluding to the long woolly hairs often encircling the calyx. The genus Iresine has been called bloodleaf and was published in 1756 by Patrick Browne.

ir'ia: this name was used as a generic name by Hendrik van Rheede tot Drakenstein in his 12-volume Hortus Indicus Malabaricus about 1693, but I have not been able to find out what it refers to. The common name of Cyperus iria is rice flatsedge or ricefield flatsedge, and it is a common species of rice paddies, so the name may have something to do with rice. There are also geographical references to an Iria Valley in several countries, Italy, India and possibly Greece. Cyperus iria was published by Linnaeus in his 1753 Species Plantarum so it could also be a nod to some mythological place or figure like Iris.

iridifo'lia: with leaves like Iris. The species Xyris iridifolia is called the iris-leaf yellow-eyed grass.

I'ris: Stearn says "named for the Greek goddess of the rainbow," and Wikipedia says "The word iris is derived from the Greek word for "rainbow," also its goddess plus messenger of the gods in the Iliad, because of the many colours of this eye part. In Greek mythology Iris was the daughter of the sea god Thaumas and the water nymph Electra, one of the Oceanids that were the daughters of the Titans Oceanus and his sister-spouse Tethys. She is mentioned in several myths carrying messages from and to the gods or running errands but has no unique mythology of her own. One of the connections between her and the rainbow is that she was said to be able to travel on rainbows while delivering messages.

irregular'is: with parts of dissimilar size.

I'satis: from the classical Greek names isatis or isatidos probably applied to the herb called woad (Isatis tinctoria) which provided the blue dye which ancient Britons used to stain their bodies, and which also was used medicinally, having ben shown to have anti-inflammatory, anti-tumour, antimicrobial, antiviral, analgesic, and antioxidant qualities. It was known as a source of dye as far back as the ancient Egyptians. The genus Isatis was published by Carl Linnaeus in 1753 and is called woad.

Iso'etes: from the Greek isos, "ever," and etas, "green," implying the character of being evergreen. Note: This is an example of the problem of defining Greek or Latin words, i.e. "ever" in this item, and "equal" in the next. Perhaps it is used with the meaning of equally green all year round, thus evergreen (?). The genus Isoetes was published by Carl Linnaeus in 1753.

Isol'epis: from the Greek isos, "equal," and lepis, "scale," referring to the glumes. The genus Isolepis was published by Robert Brown in 1810 and is called club-rush.

Isopy'rum: from Greek isos, "equal" and pyros, "wheat." Stearn says "The ancient Greek name of a Fumaria, probably transferred to these low-growing perennial herbs on account of similar foliage." Another source says "Isopyrum is the ancient Greek name for the plant's grain-like fruit." The genus Isopyrum was published by Carl Linnaeus in 1753.

Isotre'ma: William Stearn says: "from Greek isos, "equal," and trema, "hole," in allusion to the almost regular calyx-limb around the open mouth of the flower." The genus Isotrema is called Dutchman's-pipe and was published in 1819 by Constantine Rafinesque.

-is'sima/is'simum/-is'simus: a superlative suffix usually denoting "very much," or "most."

ital'ica: of or from Italy, Italian.

Ite'a: a Greek name for the willow, alluding to the willow-like leaves. The genus Itea was published by Carl Linnaeus in 1753 and is called sweetspire.

-i'um: Jaeger's Source-book says: "from Latin -ium, a suffix added to nouns and verb-stems denoting office and groups, or used as a locative suffix denoting a formation, or used as a diminutive ending."

I'va: a Latin derivation from the mint Ajuga iva, which has a similar aroma. The genus Iva is called marsh-elder and was published by Carl Linnaeus in 1753.