PLOS ONE
RESEARCH ARTICLE
Tinnea gombea (Lamiaceae), a new species
from the Sudanian savanna region, Nigeria
based on integrative evidence
Daniel A. Zhigila ID1,2*, Emmanuel I. Aigbokhan ID3, A. Muthama Muasya1
1 Department of Biological Sciences, Bolus Herbarium, University of Cape Town, Cape Town, South Africa,
2 Department of Botany, Systematics Laboratory, Gombe State University, Gombe, Gombe State, Nigeria,
3 Department of Plant Biology and Biotechnology, University of Benin, Benin City, Edo State, Nigeria
a1111111111
a1111111111
a1111111111
a1111111111
a1111111111
OPEN ACCESS
Citation: Zhigila DA, Aigbokhan EI, Muasya AM
(2023) Tinnea gombea (Lamiaceae), a new species
from the Sudanian savanna region, Nigeria based
on integrative evidence. PLoS ONE 18(3):
e0280550. https://doi.org/10.1371/journal.
pone.0280550
Editor: Tzen-Yuh Chiang, National Cheng Kung
University, TAIWAN
Received: April 23, 2022
* danielandrawus.zhigila@uct.ac.za, dazhigila@gsu.edu.ng
Abstract
Tinnea gombea, endemic to the Sudan savanna grasslands in northern Nigeria, is described
and illustrated. We used integrative evidence from morphological characters, ecology and
molecular phylogenetic data. The new species is morphologically and ecologically similar to
T. barteri and T. aethiopica, but can be readily delimited from these taxa by unique characters including a subshrub growth habit, leaves alternate to subopposite, blades lanceolate,
apically acuminate, inflorescences raceme, bearing solitary flowers in upper leaf and bract
axils, lilac to purplish dusky flowers and the inflated fruits dehiscent. The distribution and
habitat of T. gombea are also distinctive, being restricted to the Sudan savanna, while the
two most similar species are widespread in tropical Africa. Additionally, molecular phylogenetic assessments using nrITS and chloroplast trnL-F, matK and rbcL support the placement of T. gombea as a distinct species. Tinnea gombea is here assessed as Critically
Endangered due to its small population size and restriction to a small area lacking conservation prioritization.
Accepted: December 27, 2022
Published: March 16, 2023
Copyright: © 2023 Zhigila et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: DNA sequences are
available from the GenBank database, accession
numbers OP454468, OP454474, OP454489, and
OP454477 (also listed in Table 1).
Funding: DAZ, recieved research support from the
International Association of Plant Taxonomy. www.
iaptglobal.org. The funder was not involved in the
research. The funders had no role in study design,
data collection and analysis, decision to publish, or
preparation of the manuscript.
Introduction
Tinnea Kotschy ex Hook.f, is a genus in the family Lamiaceae, subfamily Scutellarioideae,
comprises 19 species native to the African continent [1, 2]. Species of the genus are found in
the west, central and east tropical and southern subtropical regions occupying the savanna
scrubs and the great Guinean forest. All species are narrow-ranged endemics except the widespread T. aethiopica Kotschy ex Hook.f. and T. barteri Gürke that extend from coastal areas of
east Africa to tropical west and central Africa and to subtropical southern Africa [2]. The subtropical regions of southern Africa recorded the highest species diversity [3].
Tinnea species are erect annual or perennial herbs, suffrutices or shrubs arising from
woody rootstock with quadrangular or terete stem transverse sections, covered with simple
hairs; leaves typically simple, opposite or ternate, covered with unicellular to glandular trichomes on both adaxial and abaxial surfaces, with glands; bracts leaf-like but smaller; inflorescence racemose, in axils of upper leaves and bracts or forming terminal spikes; flowers
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
1 / 13
PLOS ONE
Competing interests: The authors have declared
that no competing interests exist.
Tinnea gombea, a new species from the Sudan savannah
typically pedicellate, solitary or cymose, upper part of the calyx 2-lipped, short and flat but
3-lipped, broad and spoon-shaped at lower side; becoming enlarged; and nutlets inflated, with
conspicuous ridge of wings on the dorsal side [2].
The placement of the genus in Scutellarioideae was based on tuberculate corollas, exserted
stamens and inflated fruits [1–3], and later was confirmed by phylogenetic studies of Li et al.
[4] and Zhao et al. [5]. Robyns and Lebrun [1] separated the genus into two sections based on
the floral arrangements namely, section Sparsiflora with solitary or 2–3-cymes flowers not
forming distinct clusters and section Spicata with elongated spikes in axils of upper leaves and
bracts or forming clusters at the terminal head. Section Spicata was further delimited into two
subsections namely Scariosae (with two series) and Membranaceae based on calyx characters.
The calyx in the former being scarious and the latter membranous. Although Robyns and Lebrun’s [1] monograph is the most comprehensive taxonomic treatments of Tinnea, the species
delimitation and classification were completely artificial [5]. Therefore, the modern tools of
integrative phylogenetics are required to test this hypothesis.
The rapid increase of genomic sequence data has made phylogenetics an indispensable tool
for identification and classification of plants. The last two decades have witnessed growth in
molecular phylogenetic studies in Lamiaceae [e.g. 6–8], at the subfamilial and tribal level [e.g.
9–12] as well as at generic levels [e.g., 13–15]. Although Li et al. [4] and Zhao et al. [5] included
Tinnea zambesiaca Baker and T. aethiopica respectively in their molecular phylogenetic studies
of Lamiaceae, assessments of species’ phylogenetic relationships within the genus Tinnea is
lacking. According to Li et al. [4], the genus Tinnea is a close sister to Scutellaria L. The sampling of Tinnea species in these studies, however, was insufficient to allow assessing the monophyly of the genus and to contribute in understanding evolutionary relationships within
Tinnea based on molecular phylogenetic analyses.
During field trips for the preparation of a Field Guide to Herbaceous Plants of the Savanna
in Gombe State, Sudan savanna, northeastern Nigeria, we encountered noteworthy Tinnea
populations on farmlands in Akko Local Government Area. However, we were unable to key
the Tinnea collections to the descriptions from the Flora of West Tropical Africa [15], Flora of
Tropical Africa [16], a handbook of West African Weeds [17], Flora Zambesiaca [18], African
Plant Database [19] and Plants of the World Online [2]. After a detailed examination of the
specimens, we hypothesized that these populations represent an undescribed species. Herein,
we formally describe and illustrate this species new to science using morphological, ecological
and molecular evidence.
Materials and methods
Morphological study
Morphological assessments were based on herbarium specimens and our field collections. Further, protologues of all published names in the genus Tinnea from Africa and all relevant taxonomic literature [1–3, 15, 16, 20] were consulted and reviewed. To delimit the potential new
taxa from closely similar species, morphological variations were compared with herbarium
(FHI, GSUH, K, S; acronyms follow [21]) specimens including type materials on JSTOR [22]
and POWO [2]. A dissecting microscope (Leica GZ4) or stereomicroscope (Leica S9i) fitted
with digital camera (Nikon DS-5M) and eyepiece micrometer were used to measure and photograph stems, leaves, inflorescences, flowers and fruits.
Phylogenetic study
To assess the molecular phylogenetic placement of the new species within the genus Tinnea,
three chloroplast DNA markers (matK, rbcL, trnL-F) and the nuclear ITS were used following
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
2 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
Table 1. Information on the accessions used in this study. GenBank numbers for new species are in bold. matK, rbcL OP454474 and OP454477, trnL-F: OP454489, the
nuclear ITS.
ITS
trnL-F
matK
Scutellaria lateriflora L.
MK356052
1--
MK520635
MK526647
v0079576WIS
--
Korea
S. indica Blume
MH808599
MT265286
MN311856
MN192676
LuoY265
--
China
rbcL
Collector
Herbarium
Country
Tinnea aethiopica Kotschy ex Hook.f.,
--
--
KR735177
KR737558
E. DeFranco D2 K1214
EA
Kenya
T. aethiopica
--
--
KR735137
KR736734
E. DeFranco C1 K1214
EA
Kenya
T. aethiopica
--
--
KR734605
KR737516
E. DeFranco C2 K1214
EA
Kenya
T. barbata Vollesen
--
MT265260
JX518083
JX573048
G. Stafford 358
JRAU
South Africa
T. barteri Gürke
HQ911721
JX518083
HQ911385
Bendisks 050
--
--
Bester 8769
JRAU
South Africa
T. galpini Briq.
MT265261
OV140630
T. gombea Zhigila
--
--
OP454468
OP454474
D.A Zhigila 684
GSUH
Nigeria
T. gombea Zhigila
--
OP454489
--
OP454477
D.A Zhigila 685
GSUH
Nigeria
T. gracilis Gürke
--
HQ911722
HQ911386
--
A. Bjoernstad 1387
O
Tanzania
T. rhodesiana S.Moore
MF193549
MT265262
JX981418
JF265629
G. Stafford 359
JRAU
South Africa
T. rhodesiana
JF270971
MT265261
--
JX573049
G. Stafford 358
JRAU
South Africa
T. sp CP 278
MN257694
--
--
MN216517
C. Posthouwer 278
NHT
Tanzania
T. zambesiaca Baker
--
--
--
U28886
Bendisks 057
--
--
https://doi.org/10.1371/journal.pone.0280550.t001
[6, 12, 23]. Whole genomic DNA of the new species was extracted from 0.2 g of silica-gel dried
leaves using the standard CTAB protocol [24] as amended by [23]. For detailed information
on oligonucleotides and DNA markers, polymerase chain reaction mix, amplification thermal
profiles and sequencing methods used, see our previous study [23]. Other sequences available
for the genus Tinnea from other authors were downloaded from GenBank (https://www.ncbi.
nlm.nih.gov/nuccor). Two species in the closest genus Scutellaria L. (Lamiaceae), S. lateriflora
L. and S. indica Blume were selected as outgroups based on the Lamiaceae phylogenetic relationship hypothesized by [12] and [13]. Newly generated sequences were deposited on GenBank (see bold accession numbers, Table 1). Detailed information on accessions sampled for
this study are provided in Table 1.
Five sequence datasets were generated: three chloroplast DNA datasets including, matK,
rbcL, trnL-F, the nuclear ITS dataset and concatenated datasets (including all four DNA markers). Prior to the concatenation, the individual dataset was aligned using MAFFT Online service [25, 26] and manually checked and adjusted in BioEdit version 7.2.6 [27]. The individual
and concatenated datasets were phylogenetically analyzed using the Bayesian Inference and
Maximum Likelihood approaches using MrBayes version 3.2.6 x64 on XSEDE [28] and
RAxML [29] as implemented in CIPRES cluster [1–3], respectively. For the nucleotide model
substitutions of each DNA marker, the package jModelTest v.3.7 [30, 31] under the Akaike
and information criteria (AIC) was independently selected. Thus, GTR+I+ Γ for ITS, GTR+ Γ
for matK and GTR+I for rbcL and trnL-F. For details on the BI and ML analyses, refer to the
phylogenetic work in [23] except that the Markov Chain Monte Carlo analyses for both BI and
ML were run for 50,000,000 generations and sampling a tree at every 1,000th generation. The
first 0.25 of sampled generations were discarded as “burn-ins” and the 50% majority-rule consensus tree was obtained from the remaining trees.
Distribution map and conservation assessments
The distribution map was generated from specimen localities obtained from our field collections and herbarium voucher information using the naijR package version 0.4.0 as implemented in R version 4.2.0 [32]. Conservation status of a species is substantiated if one of the
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
3 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
criteria A–E outlined in the guidelines of IUCN is established [33, 34]. Hence, the conservation
status of the new species was assessed based on Criteria B (based on the area of occupancy and
extent of occurrence), C and D (restricted, with a very small population size of <2,500 individuals and known only from the type locality) of the IUCN, [34]). The Geospatial Conservation
Assessment Tool (GeoCAT; [35]; http://geocat.kew.org/) was used to quantify the Area of
occupancy (AOO) and the extent of occurrence (EOO) with the default 2 × 2 km2 size following [36].
Nomenclature
The electronic version of this article in Portable Document Format (PDF) in a work with an
ISSN or ISBN will represent a published work according to the International Code of Nomenclature for algae, fungi, and plants, and hence the new names contained in the electronic publication of a PLOS ONE article are effectively published under that Code from the electronic
edition alone, so there is no longer any need to provide printed copies.
In addition, new names contained in this work have been submitted to IPNI, from where
they will be made available to the Global Names Index. The IPNI LSIDs can be resolved and
the associated information viewed through any standard web browser by appending the LSID
contained in this publication to the prefix http://ipni.org/. The online version of this work is
archived and available from the following digital repositories PubMed Central, LOCKSS.
Results
The statistic properties of the ITS, trnL-F, matK, rbcL and combined datasets are presented in
Table 2. Even though the aligned sequence length for ITS was shorter than those of trnL-F and
matK, the percentage of parsimony informative sites was significantly higher (32.1% versus
19.5% and 2.0% respectively). Further, the number of variable sites and consistency index
recovered for each dataset reflect the lower phylogenetic signal in the chloroplast datasets versus the ITS. There are a number of shared alignment features between Scutellaria and Tinnea,
e.g. a deletion (gap) in ITS, aligned position 103–132 that is not observed in any other Tinnea
species. The already strong support values for a relationship between these two genera would
have increased if gap coding had been used.
The molecular phylogenetic relationships among the Lamiaceae taxa as indicated in the ITS
and chloroplast trees were highly congruent, although less resolved in the latter. Further, the
tree topologies obtained from BI and ML analyses were congruent. Thus, only the 50% majority-rule consensus tree obtained from the Bayesian analysis is here presented (Fig 1). Using
Scutellaria to root the tree, two strongly supported main clades are recovered: the first containing the outgroup Scutellaria species and the second containing the remaining Tinnea species.
The monophyly of Tinnea was strongly supported as revealed by both bootstrap (BS) and
Table 2. Statistical properties of the dataset used for phylogenetic analyses.
Dataset
No. taxa
alignment length
PI
CI
ITS
10
639
205 (32.1%)
0.564
variable sites
0.74
trnL-F
8
785
153 (19.5%)
0.734
0.38
matK
12
756
15 (2.0%)
0.735
0.21
rbcL
13
548
10(1.8%)
0.538
0.10
Combined
15
2728
383(14.0%)
0.43
0.2144
PI = Number and percentage of parsimony informative site, CI = Consistency index minus uninformative sites.
https://doi.org/10.1371/journal.pone.0280550.t002
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
4 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
Fig 1. A 50% majority-rule consensus tree of the genus Tinnea obtained from the Bayesian analysis of the
combined datasets of the nrITS, and matK, rbcL and trnL-F. Numbers on nodes indicate the posterior probability
and the bootstrap support values of >0.80 and >55% respectively. Note that the new species (T. gombea) is in bold
blue.
https://doi.org/10.1371/journal.pone.0280550.g001
posterior probability (PP) values of 100% and 1.00 respectively. The new species (T. gombea) is
grouped with T. barteri with strong support values (BS = 99%; PP = 0.98) and T. galpini with
moderate support value (BS = 95%; PP = 0.97).
Morphologically (Table 3; Fig 2), T. gombea is characterized by erect growth habit, 20–50
cm tall, unbranched to lax branching pattern, from taproot system. The stems are single or 2–3
in number, terete, light green or glaucous appearance due to woolly hairs covering the stem
and changes to tan with age. The leaves are alternate or subalternately arranged, attached to
the stem by subsessile petioles, blade lanceolate, about 5 × 3 cm, covered with simple trichomes
and conspicuous veins on both adaxial and abaxial surface, with abaxial surface usually light
green, adaxial surface green basally obtuse, margins entire, apex acuminate. The racemose
inflorescences have solitary flowers in upper leaf and bract axils, flowers with short pedicels,
lilac to purplish grey, upper corolla lips shorter than the lower lips, with yellowish white
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
5 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
Table 3. Morphological comparisons of T. gombea to congener species, T. aethiopica, T. barteri and T. galpini.
T. gombea
T. aethiopica
T. barteri
Growth form
subshrub
shrub
herb
T. galpini
shrub
Plant height
<50 cm tall
>50 cm tall
>50 cm tall
>50 cm tall
Branching pattern
fastigiate
virgate
virgate
virgate
Branch density
lax-branched or single-stemmed
much-branched
lax-branched
lax-branched
Leaf attachment
alternate to subopposite
opposite to subopposite
opposite to subopposite
opposite to subopposite
Leaf blade
lanceolate
orbicular
orbicular, rarely obovate
lanceolate
Petiole length (mm)
0.2–0.5
5–10
2–5
3–12
Leaf apex
acuminate
apiculate
mucronate
apiculate or obtuse
Inflorescence type
raceme
spike
spike
spike
Pedicel length (mm)
2–5
5–15
5–10
5–15
Corolla colour
lilac to purplish grey
dark reddish brown or blackish purple
purple
dark purplish brown
Fruit
dehiscent
indehiscent
indehiscent
indehiscent
Distribution range
west tropical Africa
west, east and central tropical Africa
west and central tropical Africa
southern subtropical Africa
https://doi.org/10.1371/journal.pone.0280550.t003
stamens. The fruits are inflated, ovate to orbicular, about 10 × 8 mm, tan to greyish green, dorsally winged, and dehisces into two equal halves, 1-seeded.
Discussion
A detailed morphological comparison of the new species and other allied species of Tinnea
was conducted (Table 3). Tinnea gombea is similar to T. barteri and T. aethiopica (Table 3;
[15]). However, Tinnea gombea can be distinguished from both by a series of morphological
traits such as having shorter petioles (usually to about 0.5 mm), leaves alternate to subalternately arranged, blade lanceolate, apically acuminate, shorter pedicels (usually <5 mm), lilac
to purplish dusky flowers and fruits being dehiscent (versus both T. aethiopica and T. barteri
having petioles ca. 5 mm long, orbicular or rarely long obovate leaves, apically apiculate and
mucronate respectively, longer pedicels (usually >5 mm), purplish or reddish brown to blackish purple flowers and fruits being indehiscent). Tinnea gombea best fits into Robyns and Lebrun’s [1] section Sparsiflora. It shares the solitary flowers in the axils of the upper leaves with
other species in this section. However, some characters in T. gombea overlap with species in
section Spicata too. For example, elongated racemose inflorescences and flowers solitary or
grouped as 2–5-cymes in bract axils are typical of species in section Spicata [1]. Although the
floral arrangements were the main diagnostic character of sections in Tinnea [1], there were
overlaps of these characters in species of the two sections.
Molecular phylogenetic analyses placed T. gombea as sister to a clade (Fig 1) comprising T.
barteri and three southern African taxa (T. zambesiaca, T. gracilis, T. rhodesiana). The results
of our phylogenetic analyses are generally congruent with the morphological and biogeographic patterns but do not support the infrageneric classification scheme proposed by [1].
In habitat, as for T. barteri and T. aethiopica, T. gombea also occurs in the savanna grasslands and woodlands of tropical Africa [1–3]. Within the savanna grasslands, however, T. gombea is restricted to the ecotones of loamy soil and rocky outcrops of the Sudanian savanna (Fig
3). It is noteworthy that these two species (T. aethiopica and T. barteri) were the only Tinnea
reported previously in west tropical Africa [15].
Thus, the integrative taxonomic evidence suggested by Sangster [37], here based on morphological variations (Figs 2 and 4; [1]), ecology and molecular phylogenetic position (Fig 1)
strongly support the recognition of T. gombea as an evolutionarily independent and distinct
taxon of a new species in Tinnea. Given the topology of our phylogenetic tree and the strong
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
6 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
Fig 2. Morphological features of Tinnea gombea. (A) Plant habit and habitat; (B–D) young branches bearing vegetative and
reproductive features; (E) Older branch with mature leaves, bracts and fruits; (G) closer view of dried fruits and leaves; (H) closer
view of the fluffy seed with a tuft of basal hairs. Photos by D.A. Zhigila.
https://doi.org/10.1371/journal.pone.0280550.g002
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
7 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
Fig 3. Distribution map of Tinnea gombea (black solid circle). The map was generated using naijR package version 0.4.0 as
implemented in R version 4.2.0. and is therefore for illustrative purposes only.
https://doi.org/10.1371/journal.pone.0280550.g003
morphological and ecological evidences presented, a more robust taxon and DNA region samplings are recommended to reassess the infrageneric classification of Tinnea.
Taxonomic treatment
Tinnea gombea Zhigila sp. nov. (Fig 2). [urn:lsid:ipni.org:names:77311521–1] Type
NIGERIA. Gombe State: Akko Local Government Area, in farmlands of the grassland
Sudanian savanna, elevation 620 m, 10˚ 17’ 9.96"N, 11˚ 0’ 21.6"E, 19 September 2020, D.A. Zhigila 685 (Holotype GSUH!, isotypes FHI!, K!).
Diagnosis. Tinnea gombea is most similar to T. barteri in branches being lax (2–5 in number), stems terete in cross-section, leaf blades minutely hairy on both sides, inflorescence racemose, calyx bladder-like and in ecological requirements; but differ in growth form being
annual subshrub, to about 40 cm tall, branching pattern fastigiate (versus annual herb, >50 cm
tall, virgate in T. barteri), leaf attachment alternate to 2-nate or subopposite, blade lanceolate,
leaf apex acuminate in T. gombea (versus opposite, orbicular, mucronate in T. barteri), inflorescence racemose, solitary flowers in leaf and bract axils, anthers with basal hairs (versus
spikes to 2–3-cymes, on long terminal head, anthers glabrous in T. barteri) and fruits dehiscent
(versus indehiscent in T. barteri) (Table 3).
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
8 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
Fig 4. Scanned type herbarium specimens of the most similar Tinnea species. (A) T. galpini; (B) T. aethiopica; (C) T.
barteri; and (D) T. gombea to show the similarities and variations in morphological characters. Copyright: the Board of
Trustees of the Royal Botanic Gardens, Kew, United Kingdom. Reproduced with the consent of the Royal Botanic
Gardens, Kew (K).
https://doi.org/10.1371/journal.pone.0280550.g004
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
9 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
Description. Erect annual subshrub, 15–40 cm tall, main branches 1–4, lax, fastigiate
branches, arising from a taproot system. Stems woolly, green to grey-green, sometimes purple
tinged toward the upper portion, terete. Leaves alternate or subopposite to 2-nate, shortly
(0.2–0.5 mm) petiolate to subsessile; blade narrowly ovate to lanceolate, 2–7 × 1.5–3 cm,
straight or recurved, covered with dense indument on both adaxial and abaxial sides, veins
conspicuous on the abaxial surface, inconspicuous at the adaxial surface, base obtuse, margins
entire, apex acuminate. Inflorescences are long racemes; usually arranged unilaterally, flowers
solitary and borne in bract axils, lax in the lower, clustered in the upper portion; bracts usually
subtending flowers, leaf-like (but smaller, 1–2 ×1–1.5 cm wide), alternately arranged, blade
ovate to lanceolate, recurved backward, woolly on both side, acuminate; peduncles ca. 0.5 mm
long, tan. Flowers lilac to purplish grey; calyx two unequal pairs, 5–12 ×3–5 mm, upper lobes
equal, short and rounded, lower lobes unequal, longer and rounded, densely woolly indument,
membranous; corolla tube ca. 15 mm long, woolly; stamens 4, sessile to subsessile, in two
unequal pairs, anthers yellowish, attached to the corolla tube by a tuft of woolly hairs; styles
10–12 mm long, recurved, with unequally bifid stigma. Fruits inflated and bladder-like, ovate
to orbiculate, dorsally circular wings well-developed, ca. 10 ×8 mm including the wings,
10-veined, covered with woolly hairs, tan to greyish brown, dehisces into two valves on maturity, 1-seeded. Seeds ca. 5 mm in diameter, covered with long fluffy indument.
Etymology
Tinnea gombea is named after its type locality, Gombe State, Nigeria.
Phenology
Tinnea gombea flowers from August to September and fruiting between September and
October.
Distribution and habitat
Tinnea gombea is endemic to the Sudanian savanna and is currently known from Gombe State
(Fig 3). Apparently, the species is uncommon within its area of occurrence in grasslands and
woodlands of Sudanian savanna. Usually found on abandoned farmland together with various
annual herbs and with perennial shrubs such as Spermacoce L. species, Oldenlandia corymbosa
L., Eragrostis tremula Hochst., Physalis angulata L. and Vernonia ambigua Kotschy & Peyr. It
usually grows at an elevation of about 620 m above sea level.
Conservation assessments
Tinnea gombea is known from the type locality only. We recorded <100 mature individuals in
each of the three subpopulations. We have made a concerted effort to sample the species from
other potential localities within and around abandoned farmlands in the Sudan savanna but
were unsuccessful. Therefore, further botanical surveys for possible localities for this species is
recommended. At present, the area of occupancy (AOO) of 0.5 km2 and an extent of occurrence (EOO) of 5.00 km2 were estimated for the known subpopulations. We project a continuous decline in the AOO, EOO, number of subpopulations and number of mature individuals
for T. gombea given the level of accelerated urbanization toward its area of occurrence. Further, flooding and agricultural activities (crop cultivation and overgrazing) are critical threats
to this species. Hence, preliminarily, the red list status of Critically Endangered (CR; B1, B2 (b,
c), C2 (a, b) and D) under the categories and criteria B–D of the IUCN [34] guideline is
assigned to T. gombea.
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
10 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
Additional specimen examined
NIGERIA. Gombe State: Akko Local Government Area, in farmlands of the grassland Sudanian savanna, elevation 620 m, 10˚ 17’ 6.11"N, 11˚ 1’ 55.6"E, 10 October 2020, D.A. Zhigila 684
(GSUH!, FHI!, K!).
Acknowledgments
We thank the curators of GSUH, FHI, and K for allowing access to online and physical
voucher specimens of Tinnea species. We appreciate the anonymous reviewers and PLoS ONE
Editors for the comments and suggestions that greatly improved the manuscript.
Author Contributions
Conceptualization: Daniel A. Zhigila, A. Muthama Muasya.
Data curation: Daniel A. Zhigila, Emmanuel I. Aigbokhan.
Formal analysis: Daniel A. Zhigila.
Funding acquisition: Daniel A. Zhigila, A. Muthama Muasya.
Investigation: Daniel A. Zhigila, Emmanuel I. Aigbokhan.
Methodology: Daniel A. Zhigila, Emmanuel I. Aigbokhan.
Project administration: Daniel A. Zhigila.
Resources: Daniel A. Zhigila, A. Muthama Muasya.
Software: Daniel A. Zhigila.
Supervision: A. Muthama Muasya.
Validation: Emmanuel I. Aigbokhan.
Visualization: Emmanuel I. Aigbokhan.
Writing – original draft: Daniel A. Zhigila.
Writing – review & editing: Daniel A. Zhigila, A. Muthama Muasya.
References
1.
Robyns W, Lebrun J. Essai dune monographie du genre Tinnea. Bulletin du Jardin botanique de l’État a
Bruxelles 1922; 8(1):161. https://doi.org/10.2307/3666504
2.
POWO. Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. 2022. Published on
the Internet; http://www.plantsoftheworldonline.org/ Retrieved 13 January 2022.
3.
Paton AJ, Bramley G, Ryding O, Polhill R, Harvey Y, Iwarsson M, et al. Lamiaceae (Labiatae). Flora of
Tropical East Africa: 2009;1–430.
4.
Li B, Xu WX, Tu TY, Wang ZS, Olmstead RG, Peng H, et al. Phylogenetic position of Wenchengia
(Lamiaceae): a taxonomically enigmatic and critically endangered genus. Taxon. 2016; 61:392–40.
https://doi.org/10.1002/TAX.612010
5.
Zhao F, Chen YP, Salmaki Y, Drew BT, Wilson TC, Scheen AC, et al. An updated tribal classification of
Lamiaceae based on plastome phylogenomics. BMC Biology. 2021; 19(1):2. https://doi.org/10.1186/
s12915-020-00931-z PMID: 33419433
6.
Wagstaff SJ, Hickerson L, Spangler R, Reeves PA, Olmstead RG. Phylogeny of Lamiaceae s.l. inferred
from cpDNA sequences. Plant Systematics and Evolution. 1998; 209: 265–274. https://doi.org/10.
1007/BF00985232
7.
Ryding O. Amount of calyx fibers in Lamiaceae, relation to calyx structure, phytogeny and ecology.
Plant Systematics and Evolution. 2007; 268:45–55. https://doi.org/10.1007/s00606-007-0537-y
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
11 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
8.
Yuan L, Tan G, Zhang W, Xue B, Deng J, Liu L, et al. Molecular and morphological evidence for a new
species of Pogostemon (Lamiaceae) from Hainan Island, China. PhytoKeys, 2022; 188:177–191.
https://doi.org/10.3897/phytokeys.188.76611
9.
Wagstaff SJ, Olmstead RG, Cantino PD. A phylogenetic analysis of restriction site variation in subfamily
Nepetoideae (Lamiaceae). American Journal of Botany. 1995; 82: 886–892. https://doi.org/10.1002/j.
1537-2197.1995.tb15705.x
10.
Takhtajan A. Flowering plants, 2nd ed. 2009. Berlin: Springer.
11.
Scheen AC, Bendiksby M, Ryding O, Mathiesen C, Albert VA, Lindqvist C. Molecular phylogenetics,
character evolution, and suprageneric classification of Lamioideae (Lamiaceae). Annals of Missouri
Botanical Gardens. 2010; 97: 191–192. https://doi.org/10.3417/2007174
12.
Bendiksby M, Thorbek L, Scheen AC, Lindqvist C, Ryding O. An updated phylogeny and classification
of Lamiaceae subfamily Lamioideae. Taxon. 2011; 60: 471–48. https://doi.org/10.1002/tax.602015
13.
Ryding O. Pericarp structure and phylogenetic position of the genus Wenchengia (Lamiaceae). Bot.
Jahrb. Syst. 1996; 118: 153–158.
14.
Salimov RA, Parolly G, Borsch T. Overall phylogenetic relationships of Scutellaria (Lamiaceae) shed
light on the origin of the predominantly Caucasian and Irano-Turanian S. orientalis group.–Willdenowia.
2021; 51: 395–427. https://doi.org/10.3372/wi.51.51307
15.
Hutchinson J, Dalziel JM. Flora of West Tropical Africa. Vol. I. Part 1. Second Edition. Revised by Keay
R. W. J. Crown Agents for Overseas Governments and Administrations: London. p. 295; 1972.
16.
Baker JG. Diagnoses Africanae IV. Bull. Misc. Inform., Kew. 1895: 63–75.
17.
Akobundu IO, Agyakwa CW. A hand book of West African Weeds. International Institute of Tropical
Agriculture, Ibadan, Nigeria; 1998.
18.
Paton AJ, Bramley G, Ryding O, Polhill RM, Harvey YB, Iwarsson M, et al. Flora Zambesiaca. 2013; 8
(8):1–346.
19.
African Plant Database. Conservatoire et Jardin botaniques de la Ville de Genève and South African
National Biodiversity Institute, Pretoria, version 3.4.0, 2021; "Retrieved November 2021", from <http://
africanplantdatabase.ch>
20.
Aigbokhan EI. Annotated checklist of vascular plants of southern Nigeria–a quick reference guide to the
vascular plants of southern Nigeria: a systematic approach. Uniben Press, Benin City, Nigeria; 2014.
21.
Thiers B. [Continuously Updated] Index Herbarium: a global directory of public herbaria and associated
staff. New York Botanical Garden, New York. 2022; http://sweetgum.nybg.org/science/ih/ (Accessed
in January 2022).
22.
JSTOR. Global Plants. Global Plants on JSTOR. 2021; https://plants. jstor.org/compilation/Tinnea
(accessed on 7 November 2021).
23.
Zhigila DA, Verboom GA, Muasya AM. An infrageneric classification of Thesium (Santalaceae) based
on molecular phylogenetic data. Taxon. 2020; 69(1):100–123. https://doi.org/10.1002/tax.12202.
24.
Doyle JJ, Doyle JL. A rapid DNA isolation procedure for small quantities of fresh leaf tissue. Phytochemical Bulletin, Botanical Society of America 1987; 19: 11–15.
25.
Kuraku S, Zmasek CM, Nishimura O, Katoh K. (Nucleic Acids Research 41:W22-W28) a Leaves facilitates on-demand exploration of metazoan gene family trees on MAFFT sequence alignment server with
enhanced interactivity; 2013.
26.
Katoh K, Rozewicki J, Yamada KD. MAFFT online service: Multiple sequence alignment, interactive
sequence choice and visualization. Briefings Bioinf. 2019; 20:1160–1166. https://doi.org/10.1093/bib/
bbx108 PMID: 28968734
27.
Hall TA. BioEdit: A user-friendly biological sequence alignment editor and analysis program for Windows 95/98/NT. Nucl. Acids Symp. Ser. 1999; 41: 95–98.
28.
Ronquist F, Huelsenbeck JP, Larget B, Van der Mark P, Simon D, Teslenko M. MrBayes 3: Bayesian
phylogenetic inference under mixed models. Bioinformatics 2017; 19:1572–1574. https://doi.org/10.
1093/bioinformatics/btg180
29.
Silvestro D, Michalak I. raxmlGUI: a graphical front-end for RAxML. Org Divers Evol 2012; 12:335–337.
https://doi.org/10.1007/s13127-011-0056-0
30.
Posada D, Crandall KA. Modeltest: testing the model of DNA substitution. Bioinformatics 1998; 14:817–
818. https://doi.org/10.1093/bioinformatics/14.9.817 PMID: 9918953
31.
Darriba D, Taboada GL, Doallo R, Posada D. jModelTest 2: more models, new heuristics and parallel
computing. Nature Methods 2012; 9(8): 772. https://doi.org/10.1038/nmeth.2109 PMID: 22847109
32.
R Core Team. Integrated Development for R., Inc., Boston, MA; 2022
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
12 / 13
PLOS ONE
Tinnea gombea, a new species from the Sudan savannah
33.
Lourenço-de-Moraes R, Lansac-Toha FM, Schwind LTF, Arrieira RL, Rosa RR, Terribile LC, et al. Climate change will decrease the range size of snake species under negligible protection in the Brazilian
Atlantic Forest hotspot. Scientific Reports 2019; 9:8523. https://doi.org/10.1038/s41598-019-44732-z
PMID: 31189933
34.
IUCN. Guidelines for using the IUCN Red List categories and criteria. Version 15. Standards and Petitions Subcommittee; 2022.
35.
Bachman S, Moat J, Hill AW, De la Torre J, Scott B. Supporting Red List threat assessments with GeoCAT: geospatial conservation assessment tool. ZooKeys 2011; 150:117–126. https://doi.org/10.3897/
zookeys.150.2109 PMID: 22207809
36.
Willis F, Moat J, Paton A. Defining a role for herbarium data in Red List assessments: a case study of
Plectranthus from eastern and southern tropical Africa. Biodiversity and Conservation 2003; 12:1537–
1552. https://doi.org/10.1023/A:1023679329093
37.
Sangster G. 2018. Integrative Taxonomy of Birds: The Nature and Delimitation of Species. In: Tietze D.
(eds) Bird Species. Fascinating Life Sciences. Springer, Cham. https://doi.org/10.1007/978-3-31991689-7_2
PLOS ONE | https://doi.org/10.1371/journal.pone.0280550 March 16, 2023
13 / 13