Dactyloctenium ctenioides

Landge, Shahid Nawaz, Shinde, Rajendra D., Mashau, Aluoneswi Caroline, Chandran, Manoj & Thompson, Edward John, 2025, Dactyloctenium ctenioides (Poaceae: Chloridoideae: Dactylocteniinae): brief note on the taxonomy, distribution and a new record for North America, Phytotaxa 700 (1), pp. 29-44 : 35-39

Presence of Dactyloctenium ctenioides in North America

Dr. Patti J. Anderson, a botanist with the Florida Department of Agriculture and Consumer Services Division of Plant Industry, provided the first author with images of a grass specimen collected from Dania Beach, Broward County, Florida. This exchange followed an earlier discussion about the genus Dactyloctenium , which was prompted by images published under the name D. aegyptium in a circular titled Identifying Grasses: Starting with a Few Easy Ones by Anderson (2021). The specimen, collected by an entomologist Mark Zenoble seeking to identify an insect associated with the grass, was not assigned a collection number as the collector was not a professional botanist.

In our examination of the herbarium specimen at PIHG, we confirmed and documented the first record of the obscure African species Dactyloctenium ctenioides in Florida, USA ( Figs. 3 & 4 ) as an introduction. The native range of this species includes East Africa ( Kenya, Tanzania), Madagascar, Seychelles (West Indian Ocean Islands), Mayotte Archipelago, French Administered Island ( Fig. 2 ), where it typically inhabits sea-level sand dunes and coral outcrops near the seashore with predominantly maritime distribution ( Clayton et al. 1974).

Previous introductions of related species, such as Dactyloctenium aegyptium , D. geminatum , and D. radulans , into the USA have been well-documented by Hatch (2003). These introductions were primarily linked to the cotton industry waste and ballast dumping ( Hatch 2003). It is also likely that these species were intentionally introduced as lawn grass or sand binders owing to their potential of producing stolons. However, the introduction of D. ctenioides had not been reported until now. Dr. Anderson noted that this grass is commonly found in the area i.e., Florida, and has often been identified as D. aegyptium .

This study marks the first documented occurrence of Dactyloctenium ctenioides in the USA, far outside its native range in East Africa and Western Indian Ocean Islands ( Fig. 2 ). However, the mode of introduction is not known. This discovery highlights the need for comprehensive field studies to determine the distribution of this species in Florida and neighboring states. Given the history of related species’ introductions, monitoring and managing the spread of D. ctenioides is essential to mitigate potential ecological impacts.

The identification and collection of Dactyloctenium ctenioides in Dania Beach, Florida, significantly add to the recorded flora of both the state and the country as a whole. Further research is necessary to assess the species’ distribution and potential ecological impact in the region. It is likely that this species has been misidentified as D. aegyptium not only in Florida but potentially in other parts of the region. This study underscores the importance of accurate species identification and monitoring, particularly for non-native species that may have been overlooked in past surveys.

Moreover, it is recommended that regional botanists conduct surveys to search for and identify this species in the USA. Key identification features include its granular caryopsis, open radiating spikes, anthers measuring less than 0.8 mm in length, and its annual growth habit. Genetic analyses comparing specimens from the Old World with the present findings from the New World could help further confirm the species’ identity and introduction pathways.

Understanding the reasons and mechanisms behind the introduction of African species to the North America is also critical. It is well-documented that, during the transatlantic slave trade from the 16th to 19th centuries, several Africans were forcibly transported to the Americas, possibly bringing seeds and other propagules of plants either intentionally or inadvertently. Additionally, modern air transportation serves as a vector for various seeds, enabling their survival in habitats or climatic conditions similar to their native ranges. The introduction of the species may also have occurred through the transportation of goods from East Africa, Madagascar, or the West Indian Ocean islands to America via cargo shipments.

The current finding from Florida suggests that the species could potentially be found in similar habitats across the Caribbean Islands. It is also plausible that this species exists in other parts of the world, predominantly misidentified as D. aegyptium , particularly in specimens lacking developed caryopses necessary for species confirmation. Thus, further research is needed to identify additional distinguishing features between Dactyloctenium aegyptium and D. ctenioides to facilitate easier and more accurate identification.

During the review process, one of the anonymous reviewers of this paper raised concerns regarding the identification of Dactyloctenium ctenioides and questioned its occurrence being restricted to a single locality in Florida. To address the doubt raised, we understand that the surface texture of the caryopsis is a well-established diagnostic feature in Dactyloctenium and has been consistently used to differentiate species within the genus ( Bosser 1968, Clayton et al. 1974). Moreover, Liu et al. (2005) also emphasised the importance of characters of the caryopsis in segregating genera and even species in the sub-family Chloridoideae. The features of caryopses surface remain stable across species, except in cases of interspecific hybridization.

The specimen from Florida exhibits a distinctly granular caryopsis ( Fig. 4 ), a defining trait of Dactyloctenium ctenioides , which clearly distinguishes it from D. aegyptium , whose caryopsis is transversely rugose ( Fig. 5 ). The identification follows the morphological key and descriptions provided by Clayton et al. (1974), confirming that the specimen cannot be D. aegyptium but aligns unequivocally with D. ctenioides .

As this represents the first confirmed record of Dactyloctenium ctenioides in the Americas, it serves as an important reference for future identifications. Specimens previously identified as D. aegyptium should be re-examined to verify their identity, particularly in herbarium collections and field surveys within the USA. The key to the global species of Dactyloctenium provided in the present paper can be used to accurately identify the species. This discovery highlights the need for further floristic investigations to determine the species’ potential distribution and ecological implications in the region.

Figures

FIGURE 2. Native distribution map of Dactyloctenium ctenioides in Africa and West Indian Ocean Islands (based on the data obtained from GBIF online portal). (Prepared by Dr. Caroline A. Mashau).

FIGURE 3. Herbarium specimen of Dactyloctenium ctenioides housed at PIHG herbarium, Florida, USA. (© PIHG Herbarium).

FIGURE 4. Morphology of Dactyloctenium ctenioides from Florida, USA. A. Habit. B. Anther. C & D. Spikelet. E. Caryopsis (granular surface). (based on the specimen PIHG018531). (© PIHG Herbarium).

FIGURE 5. Variations in the texture and shapes of caryopses in Dactyloctenium aegyptium and conventional caryopsis of Dactyloctenium ctenioides. A–F: Dactyloctenium aegyptium; A:Transversely rugose (conventional); B:Transversely rugose without longitudinal striations; C: Transversely rugose type with embryo not much protruded; D: Transversely crumpled or frilled-ridged caryopsis without longitudinal striations; E: Transversely frilled; F: Transversely frilled globose. G: Finely granular in Dactyloctenium ctenioides. (Photography by: Mr. Shahid Nawaz (A), Dr. Manoj Chandran (B–F), & Dr. Patti Anderson, PIHG herbarium (G)).