# Sanrobertia

Sanrobertia is a genus of flowering plants within the subtribe Symphyotrichinae of the family Asteraceae. It is monotypic, meaning there is only one species within the genus. Sanrobertia gypsophila is a rare endemic known only from Nuevo León, Mexico.

## Description

Sanrobertia gypsophila is a perennial, herbaceous plant that blooms with lilac rays and yellow disk centers during the months of August through October. It grows from a slender and woody rhizome, with blue-green stems that reach heights between about 4 and 20 cm (2 and 8 in). The plant has either tiny glands on tiny stalks called stipitate glands or it may have glands without stalks. These glands are on its upper stems, leaves, and phyllaries. Most of the plant may be slightly strigose with very short (0.1–0.5 millimeters), appressed, white, and pointed hairs.

### Leaves

Numerous alternate and simple blue-green leaves grow on the stems and branches, and they are usually somewhat clasping at their bases. Their margins (edges) are smooth, shapes are mostly oblong-lanceolate, and tips are curved slightly outward and covered with a few tiny spines. The single-nerved leaves are without a stalk (known as sessile) and are small, ranging in lengths from 4 to 7 mm and widths from 1 to 2 mm, being generally even in size and distribution along the stems.

### Flowers

The flower heads of Sanrobertia gypsophila consist of 12–16 lilac ray florets, each about 5–6 mm long and 0.8–1.2 mm wide. These surround a disk of yellow florets.

### Chromosomes

Sanrobertia gypsophila has a monoploid number (also called base number) of nine chromosomes (x = 9). The species is diploid with a total chromosome count of 18.
* S. gypsophila plant
* S. gypsophila base, stems, and leaves
* S. gypsophila flower head

## Taxonomy

Astereae 
Symphyotrichinae 
Canadanthus$^{:818}$
Ampelaster$^{:818}$
Sanrobertia$^{:1}$
Almutaster$^{:818}$
Psilactis$^{:818}$
Symphyotrichum$^{:818}$
(other subtribes) :
Cladogram references
1 2 3 4 5
Morgan, D.R.; Holland, B. (2012). "Systematics of Symphyotrichinae (Asteraceae: Astereae): Disagreements Between Two Nuclear Regions Suggest a Complex Evolutionary History". Systematic Botany. 37 (3). American Society of Plant Taxonomists: 818–832. doi:10.1600/036364412X648760. JSTOR 41515169. S2CID 84007309.
Nesom, G.L. (2018). "Aster gypsophilus (Asteraceae) Segregated as the Monotypic Genus Sanrobertia" (PDF). Phytoneuron. 2018 (25). Fort Worth, Texas: 1–8. ISSN 2153-733X. Retrieved 25 November 2020. :
The basionym of Sanrobertia gypsophila is Aster gypsophilus B.L.Turner, first published in 1974. In 1994, Guy L. Nesom reclassified it as Symphyotrichum gypsophilum (B.L.Turner) G.L.Nesom, even though the chromosome count varied from those species; he wrote that it appeared closely related to the virguloid species in the Symphyotrichum genus. In 2012, the results of further molecular analyses of Symphyotrichum and related species were published by David R. Morgan and Blake Holland which clearly placed it as separate from the Symphyotrichum genus. Thus, in 2018, Nesom published it in a monotypic genus within the subtribe Symphyotrichinae of the tribe Astereae. The cladogram shows that the genera Canadanthus, Ampelaster, and Sanrobertia are the earliest diverging members of Symphyotrichinae, developing their morphologies prior to the related species in Symphyotrichum, Almutaster, and Psilactis.

## Distribution and habitat

Sanrobertia gypsophila is a rare endemic species known only from gypsum flats and llanos near Entronque San Roberto (San Roberto Junction) in southwestern Nuevo León, Mexico, at about 1,800–2,200 meters (5,900–7,200 feet).