Denver EcoFlora Project's Journal

October EcoQuest – Cuscuta, Vampire plants

A spooky plant to look for this Halloween is Cuscuta, usually referred to as dodder but also known as strangle vine, witch’s shoelaces, and even devil’s guts. Cuscuta is also an example of a ‘vampire plant,’ or a parasitic plant that taps into other plants for all its nutrient needs. To obtain these nutrients, dodder uses a specialized root called haustoria (their ‘fangs’) to penetrate and invade the vascular tissues of plants, thus obtaining water, minerals, and carbohydrates directly from their hosts. The roots of dodders die after attachment has been made, such that the plants are entirely dependent on these hosts for survival. And just like a real vampire, dodder even needs an ‘invitation’ to step into their hosts vascular tissues, communicating through DNA with its host to lower its defenses.

Cuscuta are parasitic on a variety of different host species but have a particular affinity for crop plants and weeds such as alfalfa, many aster family members, tomato, lambsquarter, pigweed, and bindweed. Cuscuta’s common names allude to their characteristic long strands of yellowish stems that form mats and wrap around other vegetation, often appearing to ‘strangle’ their host plants. As members of the Convolvulaceae, or morning glory family, Cuscuta also exhibit flowers with the corolla lobes fused together, but the flowers are much smaller than those of a typical morning glory.

Dodder seeds can sprout without a host nearby. Once germinated, dodder seedlings use airborne chemosensory cues to grow towards nearby plants that they can tap into for food. However, if the plants do not reach a suitable host within five to 10 days of germination, the seedlings will die. Cuscuta are notoriously difficult to identify to species. There are currently four species reported from the Denver-Boulder metro area: C. approximata, C. campestris, C. cuspidata, and C. indecora. Because these plants are difficult to identify, please consult a flora to determine which species you have observed. Identifying just to genus may be necessary if flowers or fruit are unavailable.

See if you can locate some Cuscuta and help Denver Botanic Gardens by photographing as many plants as possible in the month of October. Post your findings to iNaturalist so they will automatically be added to the Denver EcoFlora Project.

Join us in celebration of the initial two years of the Denver EcoFlora Project! The EcoFlora Project was created with the goal to connect our local community with plants in an urban environment. Hear how we accomplished this through monthly EcoQuests, hosted hikes, high school internships and other outreach events, like the Amache rose project. This is a free, online event.

Register here to obtain the zoom link:
https://www.botanicgardens.org/programs/ecoflora-conference

Hope to see you there!

Not all members of the flora of Colorado produce flowers and seeds. Some, such as ferns, reproduce by spores. Spike-mosses, or Selaginella, are ferns and the sole genus in the family Selaginellaceae. Unlike some other ferns, spike-mosses have two different types of spores (megaspores and microspores) that occur in megasporangia and microsporangia located at the base of leafy branches called sporophylls. The sporophylls are only slightly differentiated from the vegetative leaves in 4-sided structures. The sporangia type can be differentiated by the color – megasporangia containing megaspores are greenish while microsporangia containing microspores are orangish.

Selaginella species are creeping plants with scale-like leaves, and can be found growing on rocky cliffs, ledges, in rocky crevices, and on rock outcroppings. The leaves of spike-mosses remain green year-round, making them a good plant to hunt for when plants have stopped blooming. There are four species of Selaginella occurring in the Denver-Boulder metro area: Selaginella densa, S. mutica, S. underwoodii, and S. weatherbiana.

Selaginella densa is easily distinguished by its densely matted growth form with short, compact branches, while the other two species are loosely matted with long, spreading branches. Selaginella densa is also our most observed spike-moss in the metro area. The other three species are more subtly distinguished among. Selaginella weatherbiana can be determined by the growth habit – at branch forks, S. weatherbiana has larger branches that continue to grow as a vegetative shoot and a shorter, smaller one that forms a fertile branch. Lastly, S. mutica leaves lack a bristle tip while S. underwoodii leaves have a short bristle tip present. This bristle tip is best viewed under a microscope or with a hand lens.

See if you can locate some Selaginella and help Denver Botanic Gardens by photographing as many plants as possible in the month of November. Post your findings to iNaturalist so they will automatically be added to the Denver EcoFlora Project.