Rare Species Guide

  Synonyms

Wulfenia bullii, Besseya bullii

  Basis for Listing

It appears that Minnesota is an important population center for this Midwestern endemic species, which is considered rare or threatened wherever it occurs. Although there are numerous known occurrences of Synthyris bullii (kitten-tails) in the southern half of the state, there has been a precipitous decline in recent decades. Many populations have been reduced to perilously low numbers, and others have been lost all together. The cause is loss or degradation of savanna habitat. In most cases, the habitats were small to begin with, usually no more than a few acres in size. They were typically inclusions in otherwise forested habitats, which were kept in a semi-open state by periodic wildfires. With the suppression of wild fires, many of these openings have grown into forests. Other losses have been attributed to urbanization as a result of the expanding metropolitan area of Minneapolis-St. Paul and surrounding suburbs.  Without statutory protection and immediate habitat restoration, the species will continue to decline. Synthyris bullii was reclassified as a threatened species in Minnesota in 1996.

  Description

Synthyris bullii produces a basal rosette of large broadly ovate velvety, heavily veined leaves. In late April or May, each sexually mature individual will produce one to several unbranched stems, which rise to a height of 15-40 cm (6-16 in.). The upper portion of each stem will be the inflorescence, with numerous small yellowish flowers arranged in a spike. The portion of the stem below the inflorescence will have small alternating bract-like leaves that partially clasp the stem. The fruit is a dry capsule with many seeds.

  Habitat

Synthyris bullii is primarily a species of oak savanna communities, though it also occurs in dry prairies and oak woodlands (including dry-mesic oak (maple) woodlands, dry-mesic oak-hickory woodlands, and dry-mesic pine-oak woodlands). The Minnesota populations are largely restricted to the bluffs and terraces of the St. Croix, Mississippi, and Minnesota River valleys, with many populations occurring in the greater Twin Cities area. Terraces of the Cannon River also support a number of populations. Plants show a preference for partial shade to full sunlight and upper slopes. Soils are most often, well-drained sandy to gravelly soil derived from alluvium or limestone bedrock.

  Biology / Life History

Synthyris bullii is a perennial herb. Flowers, which usually appear in May, are considered protandrous. This means that each flower is functionally male at first, then becomes functionally female. This arrangement is believed to maximize outcrossing, though S. bullii is self-compatible, meaning that outcrossing is not necessary to produce viable seeds. Pollinators are most often small native bees in the family Halictidae (McKone et al. 1995). This species appears to produce flowers in its second or third year. The first couple of years, the plant produces only basal leaves. Flowering plants produce larger and more numerous basal leaves than nonflowering plants.

The fruit is a dry capsule with numerous seeds. They will have matured and released their seeds by late June to mid-July. One study found fruit set to range from 25 to 93 percent, with plants in habitats exposed to full sunlight having the highest percentages (Leja and Molano-Flores 2015). Another study in Illinois (Curtis et al. 2013) found seed germination of 65-73 percent the first year, decreasing in following years. Seeds are small and flat. Wind appears to be a method of seed dispersal, though distance of dispersal is limited.

  Conservation / Management

Synthyris bullii has suffered a significant decline because of habitat loss and degradation. Threats to its habitat include gravel mining, limestone quarrying, landfills, residential and industrial development, and succession of oak savannas to forests in the absence of fire. Management techniques should be used to maintain or restore suitable habitat conditions whenever possible. Intensive management may be most urgently needed at savannas or small openings where brush is encroaching and species vigor is decreasing. Management tools may include fire, which can be effective in reducing woody vegetation and encouraging flowering. However, careful timing of prescribed fires is critical. Fire should only be used in early spring before plants appear above ground, usually during late March or early April. Once the plants appear above ground, even 2.5-5.1 cm (1-2 in.), they can be severely damaged by fire.

  Best Time to Search

The best time to identify Synthyris bullii is when it flowers in late April to late May, but the spike and basal leaves remain visible throughout the summer.

  Conservation Efforts in Minnesota

The Minnesota Biological Survey has been completed within the likely range of this species in the state. Of the many locations documented for S. bullii over the past 35 years, some populations have been destroyed, but many still survive. A number of populations occur on protected public lands, including the River Terrace Prairie Scientific and Natural Area, Afton State Park, and Wild River State Park, among others.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021

(Note: all content ©MNDNR)

  References and Additional Information

Chi, K., and B. Molano-Flores. 2016. Reproductive morphology of Synthyris bullii, a rare Midwestern endemic species, in association with habitat degradation. Journal of the Torrey Botanical Society 143(2):169-179.

Curtis, M., K. Chi, and B. Molano-Flores. 2013. Seed ecology of Synthyris bullii (Plantaginaceae), a rare endemic of the Midwestern USA. Botany 91(12):884-889.

Hufford, L., and M. McMahon. 2004. Morphological evolution and systematics of Synthyris and Besseya (Veronicaceae): a phylogenetic analysis. Systematic Botany 29(3):716-736.

Hufford, L. D. 2019. Synthyris. Pages 296-304 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 17. Oxford University Press, New York, New York.

Leja, M., K. Chi, and B. Molano-Flores. 2015. Presence and intensity of predispersal seed predation in a rare plant in response to habitat quality and population metrics. Natural Areas Journal 35(4):542-549.