Brandon Sinn Research Page
Asarum
OverviewSystematics of the flowering plant genus Asarum is a major component of my research program. To date, my work has resulted in a revised subgeneric classification of the genus, and the publication of new combinations and two new species. Here I provide web-friendly versions of diagnostic keys that I have published, as well as photographs that should prove useful for the identification of endemic North American species of Asarum.
The more than 100 Asarum species are found in north temperate forests of North America, Asia, and Europe. Phylogenetic investigations of Asarum not only provide critical foundations for improving our knowledge of genome and floral evolution, but also classification and species boundaries in this genus. For example, many morphological characters associated with the diversification of Asarum are also taxonomically informative and are useful to those working to conserve and manage these species in the wild. |
Key to Subgenera and Sections of Asarum
- Flowers non-herkogamous and autonomously self-pollinating by way of stamen movement, ovaries inferior, styles connate, abaxial calyx surface pubescent, abaxial surface of the calyx not sculptured, sepals not connate for more than half their length, leaves paired (except in A. himalaicum).
- Calyx actinomorphic, sepals conspicuously free and not forming an elongate tube; chromosome number 2n = (24)26.
- Asarum L. subgenus Asarum
- Asarum L. section Asarum
- Calyx zygomorphic, the sepals falsely connate and extending into a pseudotube; chromosome number 2n = 12.
- Asarum L. subgenus Geotaenium (F.Maek.) B.T.Sinn
- Asarum L. section Geotaenium (F.Maek.) L.Kelly
- Asarum L. subgenus Geotaenium (F.Maek.) B.T.Sinn
- Calyx zygomorphic, the sepals falsely connate and extending into a pseudotube; chromosome number 2n = 12.
- Asarum L. section Asarum
- Asarum L. subgenus Asarum
- Calyx actinomorphic, sepals conspicuously free and not forming an elongate tube; chromosome number 2n = (24)26.
- Flowers herkogamous and not autonomously self-pollinating due to lack of stamen movement (with the exception of section Asiasarum), ovaries 3/4 inferior to fully superior, styles at least partly free, abaxial calyx surface glabrous or with unicellular glandular trichomes, adaxial surface of the calyx with raised sculpturing, sepals connate and forming a tube which greatly surpasses the gyneocium, leaves solitary (with the exception of the flowering nodes of section Asiasarum species).
- Asarum L. subgenus Heterotropa (Morr. & Decne.) O.C.Schmidt
- Leaves deciduous, those of flowering nodes paired, those of non-flowering nodes solitary, adaxial calyx sculpturing of only longitudinal lines, flowers nodding and held above ground level, stamens horizontal at anthesis, chromosome number 2n = 26.
- Asarum L. section Asiasarum (F.Maek.) Araki
- Leaves evergreen, solitary, often glossy and variegated, flowers produced at ground level, adaxial calyx sculpturing often of longitudinal and horizontal lines and forming deep pits (rarely solely longitudinal lines), stamens erect at flower opening.
- Floral orifice often constricted with a membranous ring, abaxial calyx surface sculptured proximally and distally.
- Pollen white, stigmas dorsal or terminal, style extensions hardly or not surpassing stigmas and weakly bifurcate, chromosome number 2n=24.
- Asarum L. section Heterotropa (Morr. & Decne.) A.Braun
- Pollen yellow, stigmas dorsal, bifurcate style extensions long surpassing stigmas, chromosome number 2n=24, 26, or 39.
- Asarum L. section Longistylis B.T.Sinn
- Pollen white, stigmas dorsal or terminal, style extensions hardly or not surpassing stigmas and weakly bifurcate, chromosome number 2n=24.
- Floral orifice without ring, abaxial calyx surface not sculptured distally, chromosome number 2n=26.
- Asarum L. section Hexastylis (Raf.) Araki
- Floral orifice often constricted with a membranous ring, abaxial calyx surface sculptured proximally and distally.
- Leaves deciduous, those of flowering nodes paired, those of non-flowering nodes solitary, adaxial calyx sculpturing of only longitudinal lines, flowers nodding and held above ground level, stamens horizontal at anthesis, chromosome number 2n = 26.
- Asarum L. subgenus Heterotropa (Morr. & Decne.) O.C.Schmidt
Key to Section Hexastylis
1A. Trichomes of sepals and floral orifice pilose and exclusively white … 2
2A. Leaf scars widely spaced and internodes long, plants forming mats; leaves broadly hastate; sepal lobes red, often with white mottling; leaves with entire margins…………..…………………………………………A. lewisii Fernald.
2B. Internodes short, plants clumping and not forming mats; sepal lobes yellow-white, without mottling; leaves with undulate-crenulate margins ……………………………...……………………………………………A. rosei B.T.Sinn
2A. Leaf scars widely spaced and internodes long, plants forming mats; leaves broadly hastate; sepal lobes red, often with white mottling; leaves with entire margins…………..…………………………………………A. lewisii Fernald.
2B. Internodes short, plants clumping and not forming mats; sepal lobes yellow-white, without mottling; leaves with undulate-crenulate margins ……………………………...……………………………………………A. rosei B.T.Sinn
1B. Trichomes of sepals and floral orifice comprised of red or red and white cells … 3
3A. Calyx tube 3 cm or less in length, thick-walled and relatively robust, often odorless; ovary often somewhat inferior, the point of stamen insertion on the gynostemium no further from the base of the calyx tube than the height of the thecae … 4
4A. Stamen filaments broad and strap-like; thecae extrorse … 5
5A. Flower orifice not often highly constricted, or if constricted the orifice is not more than 5 mm from the widest portion of the calyx tube … 6
6A. Calyx tube greatly flared at the midpoint or higher, the floral orifice only slightly more constricted than the widest portion of the calyx tube; sepal lobes much broader than long; leaves usually variegated … 7
7A. Floral orifice nearly as wide as the interior of the calyx tube flare; calyx tube reticulations forming irregularly-shaped distally-facing pits, the longitudinal components only equaling the thickness of the calyx tube in height distally, if ever; leaves often heavily variegated. ……………………………………………..A. minus Ashe.
7B. Plants as above but with weakly variegated leaves and of frequently disturbed areas in the Sandhills region of North and South Carolina…..A. sorriei (Gaddy) B.T.Sinn.
6B. Calyx tube often flared above the middle, the floral orifice is of approximately the same width as the unflared portion of the calyx tube; sepal lobes as long or longer than their width at base; leaves often not variegated … 8
8A. Calyx lobes ± erect, much broader than long; leaves reniform to obovate-cordate, rarely variegated. Longitudinal and transverse components of the calyx tube sculpturing of approximately equal relief, the transverse components anastomosing and often not spanning the longitudinal portions forming irregularly shaped pits ….………………A. virginicum L.
8B. Longitudinal components of the calyx tube sculpturing of greater relief than the transverse components … 9
9A. Style extensions longer than the width of the stigmatic surfaces; stigmas dorsal and overhanging; calyx tube at least 1 cm in length, cylindrical, and sometimes broadly so, usually encircled by a flare distally (except in the SE portion of the range); sculpturing of the calyx tube highly developed, especially the longitudinal components; some large-flowered southern populations with slight odor…………………….....A. heterophyllum Ashe
9B. Style extensions as long as or shorter than the width of the stigmatic surfaces; stigmas nearly terminal and in notched recess; flowers extremely small, calyx tube often approximately 1 cm or less in length, cylindrical and slightly tapering or expanding toward orifice; interior sculpturing of the calyx tube poorly developed, often only the longitudinal components present. …………….…. A. naniflorum (H.L.Blomq.) B.T.Sinn.
5B. Floral orifice highly constricted, greater than 5 mm from widest point of calyx tube….A. rhombiformis (Gaddy) B.T.Sinn.
4B. Stamen filaments cylindrical; thecae latrorse or nearly so … 10
10A. Stamen filaments not strongly tapering distally, proximal and distal portion of the thecae about equally spaced; calyx tube broadest below the middle. ……………………………A. contractum (H.L.Blomq.) Barringer.
10B. Stamen filaments strongly tapering distally, thecae touching or nearly so distally; calyx fusiform and broadest at the midpoint ……………………………………………………………A. chueyi B.T.Sinn.
3A. Calyx tube 3 cm or less in length, thick-walled and relatively robust, often odorless; ovary often somewhat inferior, the point of stamen insertion on the gynostemium no further from the base of the calyx tube than the height of the thecae … 4
4A. Stamen filaments broad and strap-like; thecae extrorse … 5
5A. Flower orifice not often highly constricted, or if constricted the orifice is not more than 5 mm from the widest portion of the calyx tube … 6
6A. Calyx tube greatly flared at the midpoint or higher, the floral orifice only slightly more constricted than the widest portion of the calyx tube; sepal lobes much broader than long; leaves usually variegated … 7
7A. Floral orifice nearly as wide as the interior of the calyx tube flare; calyx tube reticulations forming irregularly-shaped distally-facing pits, the longitudinal components only equaling the thickness of the calyx tube in height distally, if ever; leaves often heavily variegated. ……………………………………………..A. minus Ashe.
7B. Plants as above but with weakly variegated leaves and of frequently disturbed areas in the Sandhills region of North and South Carolina…..A. sorriei (Gaddy) B.T.Sinn.
6B. Calyx tube often flared above the middle, the floral orifice is of approximately the same width as the unflared portion of the calyx tube; sepal lobes as long or longer than their width at base; leaves often not variegated … 8
8A. Calyx lobes ± erect, much broader than long; leaves reniform to obovate-cordate, rarely variegated. Longitudinal and transverse components of the calyx tube sculpturing of approximately equal relief, the transverse components anastomosing and often not spanning the longitudinal portions forming irregularly shaped pits ….………………A. virginicum L.
8B. Longitudinal components of the calyx tube sculpturing of greater relief than the transverse components … 9
9A. Style extensions longer than the width of the stigmatic surfaces; stigmas dorsal and overhanging; calyx tube at least 1 cm in length, cylindrical, and sometimes broadly so, usually encircled by a flare distally (except in the SE portion of the range); sculpturing of the calyx tube highly developed, especially the longitudinal components; some large-flowered southern populations with slight odor…………………….....A. heterophyllum Ashe
9B. Style extensions as long as or shorter than the width of the stigmatic surfaces; stigmas nearly terminal and in notched recess; flowers extremely small, calyx tube often approximately 1 cm or less in length, cylindrical and slightly tapering or expanding toward orifice; interior sculpturing of the calyx tube poorly developed, often only the longitudinal components present. …………….…. A. naniflorum (H.L.Blomq.) B.T.Sinn.
5B. Floral orifice highly constricted, greater than 5 mm from widest point of calyx tube….A. rhombiformis (Gaddy) B.T.Sinn.
4B. Stamen filaments cylindrical; thecae latrorse or nearly so … 10
10A. Stamen filaments not strongly tapering distally, proximal and distal portion of the thecae about equally spaced; calyx tube broadest below the middle. ……………………………A. contractum (H.L.Blomq.) Barringer.
10B. Stamen filaments strongly tapering distally, thecae touching or nearly so distally; calyx fusiform and broadest at the midpoint ……………………………………………………………A. chueyi B.T.Sinn.
3B. Calyx tube greater than 3 cm in length, thin-walled and relatively brittle, often with rancid odor; the point of stamen insertion on the gynostemium as far or further from the base of the calyx tube than the height of the thecae … 11
11A. Internodes short and leaf scars crowded on stem, plants not forming mats……………….A. shuttleworthii Britten & Baker.
11B. Internodes long and leaf scars widely spaced on stem, plants forming mats…………………A. harperi (Gaddy) Diamond.
11A. Internodes short and leaf scars crowded on stem, plants not forming mats……………….A. shuttleworthii Britten & Baker.
11B. Internodes long and leaf scars widely spaced on stem, plants forming mats…………………A. harperi (Gaddy) Diamond.
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