Neottia cordata, the lesser twayblade or heartleaf twayblade, is an orchid of upland bogs and mires. It was formerly placed in the genus Listera, but molecular phylogenetic studies have shown that Neottia nidus-avis, the bird's-nest orchid, evolved within the same group.

It is never very common but may be frequently overlooked because of its small size and a tendency to grow underneath heather on sphagnum moss.

Description Heartleaf twayblade is a herbaceous plant that has flowering stems that are between , though more often . Usually each plant has just one flowering stem, but rarely there can be as many as three. The stem is hairless, succulent, and green to purple–red; it is clasped by the leaves about a third to halfway up a flowering stem or at the top of a non-flowering stem.

The glossy green leaves are a shiny dark-green on the upper side and ovate to cordate, shaped like an egg or like a heart. They measure 0.9–4 cm long by 0.7–3.8 cm wide, although they are usually less than 2 cm long and wide. Very often there are two leaves that are almost paired, but very rarely a single stem will have as many as four leaves.

The inflorescence most often has three to fifteen blooms on the upper 1.5 to 4 cm of the stem, but they will sometimes have as many as 25 flowers. The flowers are quite small, measuring just 2–3 millimeters across. The petals are yellow-green, green, or reddish purple. The smell of the flowers is quite strong. Botanists have described it as, "truly repulsive," and resembling, "molluscs beginning to go bad."

Taxonomy Neottia cordata was given the scientific name Ophrys cordata in 1753 by Carl Linnaeus. In 1817 Louis Claude Richard moved the species to the genus Neottia, creating what became the species accepted name. Though until the 2000s it was generally placed in the genus Listera. The similarity between the two groups due to flower structure was long recognized, but formerly all the species in Neottia lacked chlorophyll. Studies of the genetics showed they should be united into one genus. Together with its genus it is classified in the family Orchidaceae. The name Neottia cordata is listed as accepted in Plants of the World Online, World Flora Online, the Database of Vascular Plants of Canada, and World Plants. However, the name Listera cordata is still encountered in some sources such as the Flora of North America.

It has no accepted subspecies, but there are two in its synonyms.

Table of Synonyms Name Year Rank Notes Bifolium cordatum 1913 species ≡ hom., nom. illeg. Cymbidium cordatum 1811 species ≡ hom. Diphryllum cordatum 1891 species ≡ hom. Distomaea cordata 1825 species ≡ hom. Epipactis cordata 1785 species ≡ hom. Helleborine cordata 1793 species ≡ hom. Listera cordata 1813 species ≡ hom. Listera cordata f. appendiculata 1946 form = het. Listera cordata var. chlorantha 1925 variety = het. Listera cordata f. crassa 1957 form = het. Listera cordata f. disjuncta 1946 form = het. Listera cordata subsp. japonica 1971 subspecies = het. Listera cordata var. japonica 1938 variety = het. Listera cordata subsp. nephrophylla 1965 subspecies = het. Listera cordata var. nephrophylla 1937 variety = het. Listera cordata f. pallida 1889 form = het. Listera cordata f. rubescens 1995 form = het. Listera cordata f. tenuis 1957 form = het. Listera cordata f. tetraphylla 1984 form = het. Listera cordata f. trifolia 1972 form = het. Listera cordata f. trifolia 1995 form = het., nom. illeg. Listera cordata lusus trifolia 1907 sport = het. Listera cordata f. variegata 1995 form = het. Listera cordata f. viridens 1995 form = het. Listera nephrophylla 1900 species = het. Neottia cordata f. rubescens 2019 form = het. Neottia nephrophylla 1995 species = het. Ophrys cordata 1753 species ≡ hom. Ophrys nephrophylla 1905 species = het. Pollinirhiza cordata 1867 species ≡ hom. Serapias cordata 1821 species ≡ hom. Notes: ≡ homotypic synonym; = heterotypic synonym

Names The species name, cordata, is Botanical Latin meaning "heart shaped". Similarly, it is known by the common name heart-leaved twayblade. Other common names include heartleaf twayblade, western heart-leaved twayblade, lesser twayblade, and simply twayblade. Although, Neottia ovata is also known as twayblade.

Distribution It has a circumpolar distribution being found in Europe, Asia and large parts of North America. In the United Kingdom its distribution is largely western and northern, becoming most common in the western Highlands of Scotland, Snowdonia in Wales, and the Lake District and the Pennines in England, but also a small population as far south as Exmoor.

Ecology The flowers produce nectar and are pollinated principally by fungus gnats in the groups Mycetophilidae and Sciaridae.

Mycorrhizal partners are almost exclusively fungi in the Sebacinales clade Serendipitaceae. There may also be some association with Ceratobasidiaceae and/or Tulasnellaceae.

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